Sample of 3 from 5: Permutation or Combination?
I answered this question correctly using combinations rather than permutations. Is my solution valid, or am I misreading the question?
"A sample of size 3 is drawn at random and without replacement from the population ${1, 2, 3, 4, 5}$. What is the probability that the range of the sample is equal to 3?"
My logic: Because we are interested in the events where the range is three, I concluded that the cardinality of the sample N from the population $P$ is #$(N) = 4$ because $N = {(1, 2, 4), (1, 3, 4), (2, 3, 5), (2, 4, 5)}$.
So then the $P($range$ = 3) =dfrac{4}{5 choose 3} = dfrac{4}{10}$.
Solution: There are six possible orderings for both $(1,2,4)$ and $(1,3,4)$, which is also true for both $(2,3,5)$ and $(2,4,5)$. So there are 24 ways to select the three good sets and $(5)(4)(3)= 60$ ways to select three from $P$. So $dfrac{24}{60} = dfrac{4}{10}$
Does the phrase "without replacement" imply one at a time? Or is there something in the phrasing of this question that should signal to me to use permutations rather than combinations? I was under the impression that the order they are chosen doesn't matter because the range relies on the two numbers being chosen in such a way that they are the max and minimum and the difference is 3.
probability combinatorics permutations combinations
add a comment |
I answered this question correctly using combinations rather than permutations. Is my solution valid, or am I misreading the question?
"A sample of size 3 is drawn at random and without replacement from the population ${1, 2, 3, 4, 5}$. What is the probability that the range of the sample is equal to 3?"
My logic: Because we are interested in the events where the range is three, I concluded that the cardinality of the sample N from the population $P$ is #$(N) = 4$ because $N = {(1, 2, 4), (1, 3, 4), (2, 3, 5), (2, 4, 5)}$.
So then the $P($range$ = 3) =dfrac{4}{5 choose 3} = dfrac{4}{10}$.
Solution: There are six possible orderings for both $(1,2,4)$ and $(1,3,4)$, which is also true for both $(2,3,5)$ and $(2,4,5)$. So there are 24 ways to select the three good sets and $(5)(4)(3)= 60$ ways to select three from $P$. So $dfrac{24}{60} = dfrac{4}{10}$
Does the phrase "without replacement" imply one at a time? Or is there something in the phrasing of this question that should signal to me to use permutations rather than combinations? I was under the impression that the order they are chosen doesn't matter because the range relies on the two numbers being chosen in such a way that they are the max and minimum and the difference is 3.
probability combinatorics permutations combinations
2
"Without replacement" means that a sampled object is withdrawn from the population, so it can't be sampled a second time. That is, there are no duplicates. So, order doesn't matter. I think your answer is correct. Why do you have any doubts?
– saulspatz
Nov 28 '18 at 5:09
Thanks for your comment. I have doubts because the solution is different than how I got the answer, and it's possible to get the right answer with the wrong logic. I suppose permutations and combinations are logically equivalent as 5choose3 * 6 = 60?
– TYBG
Nov 28 '18 at 5:38
1
The order in which the items re drawn doesn't affect the range, so your solution is correct. Of course, one can also take order into account, and arrive at the same answer, as in the solution you quote. I prefer your solution, for whatever that's worth.
– saulspatz
Nov 28 '18 at 5:43
add a comment |
I answered this question correctly using combinations rather than permutations. Is my solution valid, or am I misreading the question?
"A sample of size 3 is drawn at random and without replacement from the population ${1, 2, 3, 4, 5}$. What is the probability that the range of the sample is equal to 3?"
My logic: Because we are interested in the events where the range is three, I concluded that the cardinality of the sample N from the population $P$ is #$(N) = 4$ because $N = {(1, 2, 4), (1, 3, 4), (2, 3, 5), (2, 4, 5)}$.
So then the $P($range$ = 3) =dfrac{4}{5 choose 3} = dfrac{4}{10}$.
Solution: There are six possible orderings for both $(1,2,4)$ and $(1,3,4)$, which is also true for both $(2,3,5)$ and $(2,4,5)$. So there are 24 ways to select the three good sets and $(5)(4)(3)= 60$ ways to select three from $P$. So $dfrac{24}{60} = dfrac{4}{10}$
Does the phrase "without replacement" imply one at a time? Or is there something in the phrasing of this question that should signal to me to use permutations rather than combinations? I was under the impression that the order they are chosen doesn't matter because the range relies on the two numbers being chosen in such a way that they are the max and minimum and the difference is 3.
probability combinatorics permutations combinations
I answered this question correctly using combinations rather than permutations. Is my solution valid, or am I misreading the question?
"A sample of size 3 is drawn at random and without replacement from the population ${1, 2, 3, 4, 5}$. What is the probability that the range of the sample is equal to 3?"
My logic: Because we are interested in the events where the range is three, I concluded that the cardinality of the sample N from the population $P$ is #$(N) = 4$ because $N = {(1, 2, 4), (1, 3, 4), (2, 3, 5), (2, 4, 5)}$.
So then the $P($range$ = 3) =dfrac{4}{5 choose 3} = dfrac{4}{10}$.
Solution: There are six possible orderings for both $(1,2,4)$ and $(1,3,4)$, which is also true for both $(2,3,5)$ and $(2,4,5)$. So there are 24 ways to select the three good sets and $(5)(4)(3)= 60$ ways to select three from $P$. So $dfrac{24}{60} = dfrac{4}{10}$
Does the phrase "without replacement" imply one at a time? Or is there something in the phrasing of this question that should signal to me to use permutations rather than combinations? I was under the impression that the order they are chosen doesn't matter because the range relies on the two numbers being chosen in such a way that they are the max and minimum and the difference is 3.
probability combinatorics permutations combinations
probability combinatorics permutations combinations
asked Nov 28 '18 at 3:57
TYBGTYBG
356
356
2
"Without replacement" means that a sampled object is withdrawn from the population, so it can't be sampled a second time. That is, there are no duplicates. So, order doesn't matter. I think your answer is correct. Why do you have any doubts?
– saulspatz
Nov 28 '18 at 5:09
Thanks for your comment. I have doubts because the solution is different than how I got the answer, and it's possible to get the right answer with the wrong logic. I suppose permutations and combinations are logically equivalent as 5choose3 * 6 = 60?
– TYBG
Nov 28 '18 at 5:38
1
The order in which the items re drawn doesn't affect the range, so your solution is correct. Of course, one can also take order into account, and arrive at the same answer, as in the solution you quote. I prefer your solution, for whatever that's worth.
– saulspatz
Nov 28 '18 at 5:43
add a comment |
2
"Without replacement" means that a sampled object is withdrawn from the population, so it can't be sampled a second time. That is, there are no duplicates. So, order doesn't matter. I think your answer is correct. Why do you have any doubts?
– saulspatz
Nov 28 '18 at 5:09
Thanks for your comment. I have doubts because the solution is different than how I got the answer, and it's possible to get the right answer with the wrong logic. I suppose permutations and combinations are logically equivalent as 5choose3 * 6 = 60?
– TYBG
Nov 28 '18 at 5:38
1
The order in which the items re drawn doesn't affect the range, so your solution is correct. Of course, one can also take order into account, and arrive at the same answer, as in the solution you quote. I prefer your solution, for whatever that's worth.
– saulspatz
Nov 28 '18 at 5:43
2
2
"Without replacement" means that a sampled object is withdrawn from the population, so it can't be sampled a second time. That is, there are no duplicates. So, order doesn't matter. I think your answer is correct. Why do you have any doubts?
– saulspatz
Nov 28 '18 at 5:09
"Without replacement" means that a sampled object is withdrawn from the population, so it can't be sampled a second time. That is, there are no duplicates. So, order doesn't matter. I think your answer is correct. Why do you have any doubts?
– saulspatz
Nov 28 '18 at 5:09
Thanks for your comment. I have doubts because the solution is different than how I got the answer, and it's possible to get the right answer with the wrong logic. I suppose permutations and combinations are logically equivalent as 5choose3 * 6 = 60?
– TYBG
Nov 28 '18 at 5:38
Thanks for your comment. I have doubts because the solution is different than how I got the answer, and it's possible to get the right answer with the wrong logic. I suppose permutations and combinations are logically equivalent as 5choose3 * 6 = 60?
– TYBG
Nov 28 '18 at 5:38
1
1
The order in which the items re drawn doesn't affect the range, so your solution is correct. Of course, one can also take order into account, and arrive at the same answer, as in the solution you quote. I prefer your solution, for whatever that's worth.
– saulspatz
Nov 28 '18 at 5:43
The order in which the items re drawn doesn't affect the range, so your solution is correct. Of course, one can also take order into account, and arrive at the same answer, as in the solution you quote. I prefer your solution, for whatever that's worth.
– saulspatz
Nov 28 '18 at 5:43
add a comment |
1 Answer
1
active
oldest
votes
Is my solution valid, or am I misreading the question?
Your solution is valid.
Or is there something in the phrasing of this question that should signal to me to use permutations rather than combinations? I was under the impression that the order they are chosen doesn't matter because the range relies on the two numbers being chosen in such a way that they are the max and minimum and the difference is 3.
You counted ways to obtain a combination with a range of 3 (maximum-minimum) when selecting three numbers. [Select a minumum, select a middle, select a maximum such that maximum-minum=3 vs. select any three from the five numbers.]
$$dfrac{{^2mathrm C_1}{^2mathrm C_1}{^1mathrm C_1}}{^5mathrm C_3}$$
They counted the way to obtain a permutation with a range of 3 (maximum-minimum) when selecting and arranging three numbers.
$$dfrac{{^2mathrm C_1}{^2mathrm C_1}{^1mathrm C_1}~ 3!}{^5mathrm C_3~ 3!}$$
Well, now you see that here, as often is the case, the extra effort of counting ways to arrange is redundant because the common factor cancels.
Remark: Generally when order is important (for the event), then the probability is a ratio of permutation to combination. However, when order is not important (for the event), then the probability may equally be either a ratio of combinations, or a ratio of permutations. (Assuming all atomic outcomes being counted are equally probable)
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
});
});
}, "mathjax-editing");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "69"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3016694%2fsample-of-3-from-5-permutation-or-combination%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Is my solution valid, or am I misreading the question?
Your solution is valid.
Or is there something in the phrasing of this question that should signal to me to use permutations rather than combinations? I was under the impression that the order they are chosen doesn't matter because the range relies on the two numbers being chosen in such a way that they are the max and minimum and the difference is 3.
You counted ways to obtain a combination with a range of 3 (maximum-minimum) when selecting three numbers. [Select a minumum, select a middle, select a maximum such that maximum-minum=3 vs. select any three from the five numbers.]
$$dfrac{{^2mathrm C_1}{^2mathrm C_1}{^1mathrm C_1}}{^5mathrm C_3}$$
They counted the way to obtain a permutation with a range of 3 (maximum-minimum) when selecting and arranging three numbers.
$$dfrac{{^2mathrm C_1}{^2mathrm C_1}{^1mathrm C_1}~ 3!}{^5mathrm C_3~ 3!}$$
Well, now you see that here, as often is the case, the extra effort of counting ways to arrange is redundant because the common factor cancels.
Remark: Generally when order is important (for the event), then the probability is a ratio of permutation to combination. However, when order is not important (for the event), then the probability may equally be either a ratio of combinations, or a ratio of permutations. (Assuming all atomic outcomes being counted are equally probable)
add a comment |
Is my solution valid, or am I misreading the question?
Your solution is valid.
Or is there something in the phrasing of this question that should signal to me to use permutations rather than combinations? I was under the impression that the order they are chosen doesn't matter because the range relies on the two numbers being chosen in such a way that they are the max and minimum and the difference is 3.
You counted ways to obtain a combination with a range of 3 (maximum-minimum) when selecting three numbers. [Select a minumum, select a middle, select a maximum such that maximum-minum=3 vs. select any three from the five numbers.]
$$dfrac{{^2mathrm C_1}{^2mathrm C_1}{^1mathrm C_1}}{^5mathrm C_3}$$
They counted the way to obtain a permutation with a range of 3 (maximum-minimum) when selecting and arranging three numbers.
$$dfrac{{^2mathrm C_1}{^2mathrm C_1}{^1mathrm C_1}~ 3!}{^5mathrm C_3~ 3!}$$
Well, now you see that here, as often is the case, the extra effort of counting ways to arrange is redundant because the common factor cancels.
Remark: Generally when order is important (for the event), then the probability is a ratio of permutation to combination. However, when order is not important (for the event), then the probability may equally be either a ratio of combinations, or a ratio of permutations. (Assuming all atomic outcomes being counted are equally probable)
add a comment |
Is my solution valid, or am I misreading the question?
Your solution is valid.
Or is there something in the phrasing of this question that should signal to me to use permutations rather than combinations? I was under the impression that the order they are chosen doesn't matter because the range relies on the two numbers being chosen in such a way that they are the max and minimum and the difference is 3.
You counted ways to obtain a combination with a range of 3 (maximum-minimum) when selecting three numbers. [Select a minumum, select a middle, select a maximum such that maximum-minum=3 vs. select any three from the five numbers.]
$$dfrac{{^2mathrm C_1}{^2mathrm C_1}{^1mathrm C_1}}{^5mathrm C_3}$$
They counted the way to obtain a permutation with a range of 3 (maximum-minimum) when selecting and arranging three numbers.
$$dfrac{{^2mathrm C_1}{^2mathrm C_1}{^1mathrm C_1}~ 3!}{^5mathrm C_3~ 3!}$$
Well, now you see that here, as often is the case, the extra effort of counting ways to arrange is redundant because the common factor cancels.
Remark: Generally when order is important (for the event), then the probability is a ratio of permutation to combination. However, when order is not important (for the event), then the probability may equally be either a ratio of combinations, or a ratio of permutations. (Assuming all atomic outcomes being counted are equally probable)
Is my solution valid, or am I misreading the question?
Your solution is valid.
Or is there something in the phrasing of this question that should signal to me to use permutations rather than combinations? I was under the impression that the order they are chosen doesn't matter because the range relies on the two numbers being chosen in such a way that they are the max and minimum and the difference is 3.
You counted ways to obtain a combination with a range of 3 (maximum-minimum) when selecting three numbers. [Select a minumum, select a middle, select a maximum such that maximum-minum=3 vs. select any three from the five numbers.]
$$dfrac{{^2mathrm C_1}{^2mathrm C_1}{^1mathrm C_1}}{^5mathrm C_3}$$
They counted the way to obtain a permutation with a range of 3 (maximum-minimum) when selecting and arranging three numbers.
$$dfrac{{^2mathrm C_1}{^2mathrm C_1}{^1mathrm C_1}~ 3!}{^5mathrm C_3~ 3!}$$
Well, now you see that here, as often is the case, the extra effort of counting ways to arrange is redundant because the common factor cancels.
Remark: Generally when order is important (for the event), then the probability is a ratio of permutation to combination. However, when order is not important (for the event), then the probability may equally be either a ratio of combinations, or a ratio of permutations. (Assuming all atomic outcomes being counted are equally probable)
edited Nov 30 '18 at 9:47
answered Nov 29 '18 at 4:13
Graham KempGraham Kemp
84.7k43378
84.7k43378
add a comment |
add a comment |
Thanks for contributing an answer to Mathematics Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3016694%2fsample-of-3-from-5-permutation-or-combination%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
2
"Without replacement" means that a sampled object is withdrawn from the population, so it can't be sampled a second time. That is, there are no duplicates. So, order doesn't matter. I think your answer is correct. Why do you have any doubts?
– saulspatz
Nov 28 '18 at 5:09
Thanks for your comment. I have doubts because the solution is different than how I got the answer, and it's possible to get the right answer with the wrong logic. I suppose permutations and combinations are logically equivalent as 5choose3 * 6 = 60?
– TYBG
Nov 28 '18 at 5:38
1
The order in which the items re drawn doesn't affect the range, so your solution is correct. Of course, one can also take order into account, and arrive at the same answer, as in the solution you quote. I prefer your solution, for whatever that's worth.
– saulspatz
Nov 28 '18 at 5:43