Steadily accumulating number formula
$begingroup$
This is quite likely a super simple question, but I lack the descriptive power to be able to find the answer on Google!
Consider the following two number sequences:
00, 10, 20, 30, 40, 50, 60, 70, 80, 90
45, 45, 45, 45, 45, 45, 45, 45, 45, 45
Both sequences have a total value of 450, but one accumulates steadily in multiples of 10, whilst the second remains constant at 45.
The second is easy to ascertain, divide the total value by the number of instances in the list. But the first sequence I'm stuck on - can anyone help me understand the formula for ascertaining the accumulation value (in this instance 10) from 0?
My goal is to be able to take any number and divide it x
number of times, with the first number in the sequence being 0 and steadily increasing - apportioning greater and greater values to those later in the sequence.
sequences-and-series
New contributor
$endgroup$
add a comment |
$begingroup$
This is quite likely a super simple question, but I lack the descriptive power to be able to find the answer on Google!
Consider the following two number sequences:
00, 10, 20, 30, 40, 50, 60, 70, 80, 90
45, 45, 45, 45, 45, 45, 45, 45, 45, 45
Both sequences have a total value of 450, but one accumulates steadily in multiples of 10, whilst the second remains constant at 45.
The second is easy to ascertain, divide the total value by the number of instances in the list. But the first sequence I'm stuck on - can anyone help me understand the formula for ascertaining the accumulation value (in this instance 10) from 0?
My goal is to be able to take any number and divide it x
number of times, with the first number in the sequence being 0 and steadily increasing - apportioning greater and greater values to those later in the sequence.
sequences-and-series
New contributor
$endgroup$
$begingroup$
The keywords you need are "arithmetic progression".
$endgroup$
– FredH
Mar 25 at 4:33
$begingroup$
Thank you, that instantly helps a lot with my googling!
$endgroup$
– Ryan Gillies
Mar 25 at 4:39
add a comment |
$begingroup$
This is quite likely a super simple question, but I lack the descriptive power to be able to find the answer on Google!
Consider the following two number sequences:
00, 10, 20, 30, 40, 50, 60, 70, 80, 90
45, 45, 45, 45, 45, 45, 45, 45, 45, 45
Both sequences have a total value of 450, but one accumulates steadily in multiples of 10, whilst the second remains constant at 45.
The second is easy to ascertain, divide the total value by the number of instances in the list. But the first sequence I'm stuck on - can anyone help me understand the formula for ascertaining the accumulation value (in this instance 10) from 0?
My goal is to be able to take any number and divide it x
number of times, with the first number in the sequence being 0 and steadily increasing - apportioning greater and greater values to those later in the sequence.
sequences-and-series
New contributor
$endgroup$
This is quite likely a super simple question, but I lack the descriptive power to be able to find the answer on Google!
Consider the following two number sequences:
00, 10, 20, 30, 40, 50, 60, 70, 80, 90
45, 45, 45, 45, 45, 45, 45, 45, 45, 45
Both sequences have a total value of 450, but one accumulates steadily in multiples of 10, whilst the second remains constant at 45.
The second is easy to ascertain, divide the total value by the number of instances in the list. But the first sequence I'm stuck on - can anyone help me understand the formula for ascertaining the accumulation value (in this instance 10) from 0?
My goal is to be able to take any number and divide it x
number of times, with the first number in the sequence being 0 and steadily increasing - apportioning greater and greater values to those later in the sequence.
sequences-and-series
sequences-and-series
New contributor
New contributor
New contributor
asked Mar 25 at 4:24
Ryan GilliesRyan Gillies
182
182
New contributor
New contributor
$begingroup$
The keywords you need are "arithmetic progression".
$endgroup$
– FredH
Mar 25 at 4:33
$begingroup$
Thank you, that instantly helps a lot with my googling!
$endgroup$
– Ryan Gillies
Mar 25 at 4:39
add a comment |
$begingroup$
The keywords you need are "arithmetic progression".
$endgroup$
– FredH
Mar 25 at 4:33
$begingroup$
Thank you, that instantly helps a lot with my googling!
$endgroup$
– Ryan Gillies
Mar 25 at 4:39
$begingroup$
The keywords you need are "arithmetic progression".
$endgroup$
– FredH
Mar 25 at 4:33
$begingroup$
The keywords you need are "arithmetic progression".
$endgroup$
– FredH
Mar 25 at 4:33
$begingroup$
Thank you, that instantly helps a lot with my googling!
$endgroup$
– Ryan Gillies
Mar 25 at 4:39
$begingroup$
Thank you, that instantly helps a lot with my googling!
$endgroup$
– Ryan Gillies
Mar 25 at 4:39
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
It's an arithmetic sequence (i. e. every next element is created from the previous with adding the same number) with the well-known formula for its sum
$$a_1 + a_2 + cdots + a_n = {n over 2}(a_1+a_n)$$
So, as $a_1= 0, n = 10, $ and $ a_{10} = 90$ you will obtain
$$00 + 10 +20 + cdots + 90 = {10over2}(0 + 90)= 5cdot 90 = 450$$
Addendum:
If you know the first element ($a_1$), number of elements ($n$) and their sum ($s$), you may obtain the last element ($a_n$) by substituting the known values into the formula, and then isolate $a_n$:
$$a_n = {2sover n}-a_1$$
You may then compute the difference $d$ between adjacent members as
$$d = {a_n-a_1over n-1}$$
to consecutively obtain members between $a_1$ and $a_n$:
begin{aligned}
a_2 &= a_1+d\a_3 &= a_2+d\
&cdots
end{aligned}
(To the question in your comment.)
$endgroup$
$begingroup$
Using this approach it appears I need to know the answer toan
(90) - if I only havea1
(0) and 450, could it still be done?
$endgroup$
– Ryan Gillies
Mar 25 at 4:43
$begingroup$
@Ryan You have the values for n, $a_1$, and the sum. That leaves $a_n$ as the only variable. You can solve for $a_n$ to get $a_n=frac{2}{n}(x)-a_1$ where $x$ is the sum (450 in your case).
$endgroup$
– Jacob Jones
Mar 25 at 4:57
$begingroup$
Sorry yes you're right I forgot to include that in my comment, I will always know number of elements (n) first number in sequence (a1) and the sum (in this example 450). What I don't know is the last number in sequence (an).
$endgroup$
– Ryan Gillies
Mar 25 at 4:57
$begingroup$
You need know also the number of elements ($n$) to substitute it to the given formula, because without this you may write the sum $450$ in many different ways, e. g. $450 = 0 + 450 = 0 + 150 + 300 = 0 +45 +90 +135 +180$.
$endgroup$
– MarianD
Mar 25 at 5:00
$begingroup$
Nailed it, understood perfectly! Thank you so much for your help MarianD and @JacobJones!
$endgroup$
– Ryan Gillies
Mar 25 at 5:01
add a comment |
$begingroup$
$$sumlimits_{i=0}^9 10 i = 10 sumlimits_{i=0}^9 i = 10 left[ frac{(9+0)(9+1)}{2} right] =450$$
$endgroup$
add a comment |
Your Answer
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2 Answers
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2 Answers
2
active
oldest
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votes
$begingroup$
It's an arithmetic sequence (i. e. every next element is created from the previous with adding the same number) with the well-known formula for its sum
$$a_1 + a_2 + cdots + a_n = {n over 2}(a_1+a_n)$$
So, as $a_1= 0, n = 10, $ and $ a_{10} = 90$ you will obtain
$$00 + 10 +20 + cdots + 90 = {10over2}(0 + 90)= 5cdot 90 = 450$$
Addendum:
If you know the first element ($a_1$), number of elements ($n$) and their sum ($s$), you may obtain the last element ($a_n$) by substituting the known values into the formula, and then isolate $a_n$:
$$a_n = {2sover n}-a_1$$
You may then compute the difference $d$ between adjacent members as
$$d = {a_n-a_1over n-1}$$
to consecutively obtain members between $a_1$ and $a_n$:
begin{aligned}
a_2 &= a_1+d\a_3 &= a_2+d\
&cdots
end{aligned}
(To the question in your comment.)
$endgroup$
$begingroup$
Using this approach it appears I need to know the answer toan
(90) - if I only havea1
(0) and 450, could it still be done?
$endgroup$
– Ryan Gillies
Mar 25 at 4:43
$begingroup$
@Ryan You have the values for n, $a_1$, and the sum. That leaves $a_n$ as the only variable. You can solve for $a_n$ to get $a_n=frac{2}{n}(x)-a_1$ where $x$ is the sum (450 in your case).
$endgroup$
– Jacob Jones
Mar 25 at 4:57
$begingroup$
Sorry yes you're right I forgot to include that in my comment, I will always know number of elements (n) first number in sequence (a1) and the sum (in this example 450). What I don't know is the last number in sequence (an).
$endgroup$
– Ryan Gillies
Mar 25 at 4:57
$begingroup$
You need know also the number of elements ($n$) to substitute it to the given formula, because without this you may write the sum $450$ in many different ways, e. g. $450 = 0 + 450 = 0 + 150 + 300 = 0 +45 +90 +135 +180$.
$endgroup$
– MarianD
Mar 25 at 5:00
$begingroup$
Nailed it, understood perfectly! Thank you so much for your help MarianD and @JacobJones!
$endgroup$
– Ryan Gillies
Mar 25 at 5:01
add a comment |
$begingroup$
It's an arithmetic sequence (i. e. every next element is created from the previous with adding the same number) with the well-known formula for its sum
$$a_1 + a_2 + cdots + a_n = {n over 2}(a_1+a_n)$$
So, as $a_1= 0, n = 10, $ and $ a_{10} = 90$ you will obtain
$$00 + 10 +20 + cdots + 90 = {10over2}(0 + 90)= 5cdot 90 = 450$$
Addendum:
If you know the first element ($a_1$), number of elements ($n$) and their sum ($s$), you may obtain the last element ($a_n$) by substituting the known values into the formula, and then isolate $a_n$:
$$a_n = {2sover n}-a_1$$
You may then compute the difference $d$ between adjacent members as
$$d = {a_n-a_1over n-1}$$
to consecutively obtain members between $a_1$ and $a_n$:
begin{aligned}
a_2 &= a_1+d\a_3 &= a_2+d\
&cdots
end{aligned}
(To the question in your comment.)
$endgroup$
$begingroup$
Using this approach it appears I need to know the answer toan
(90) - if I only havea1
(0) and 450, could it still be done?
$endgroup$
– Ryan Gillies
Mar 25 at 4:43
$begingroup$
@Ryan You have the values for n, $a_1$, and the sum. That leaves $a_n$ as the only variable. You can solve for $a_n$ to get $a_n=frac{2}{n}(x)-a_1$ where $x$ is the sum (450 in your case).
$endgroup$
– Jacob Jones
Mar 25 at 4:57
$begingroup$
Sorry yes you're right I forgot to include that in my comment, I will always know number of elements (n) first number in sequence (a1) and the sum (in this example 450). What I don't know is the last number in sequence (an).
$endgroup$
– Ryan Gillies
Mar 25 at 4:57
$begingroup$
You need know also the number of elements ($n$) to substitute it to the given formula, because without this you may write the sum $450$ in many different ways, e. g. $450 = 0 + 450 = 0 + 150 + 300 = 0 +45 +90 +135 +180$.
$endgroup$
– MarianD
Mar 25 at 5:00
$begingroup$
Nailed it, understood perfectly! Thank you so much for your help MarianD and @JacobJones!
$endgroup$
– Ryan Gillies
Mar 25 at 5:01
add a comment |
$begingroup$
It's an arithmetic sequence (i. e. every next element is created from the previous with adding the same number) with the well-known formula for its sum
$$a_1 + a_2 + cdots + a_n = {n over 2}(a_1+a_n)$$
So, as $a_1= 0, n = 10, $ and $ a_{10} = 90$ you will obtain
$$00 + 10 +20 + cdots + 90 = {10over2}(0 + 90)= 5cdot 90 = 450$$
Addendum:
If you know the first element ($a_1$), number of elements ($n$) and their sum ($s$), you may obtain the last element ($a_n$) by substituting the known values into the formula, and then isolate $a_n$:
$$a_n = {2sover n}-a_1$$
You may then compute the difference $d$ between adjacent members as
$$d = {a_n-a_1over n-1}$$
to consecutively obtain members between $a_1$ and $a_n$:
begin{aligned}
a_2 &= a_1+d\a_3 &= a_2+d\
&cdots
end{aligned}
(To the question in your comment.)
$endgroup$
It's an arithmetic sequence (i. e. every next element is created from the previous with adding the same number) with the well-known formula for its sum
$$a_1 + a_2 + cdots + a_n = {n over 2}(a_1+a_n)$$
So, as $a_1= 0, n = 10, $ and $ a_{10} = 90$ you will obtain
$$00 + 10 +20 + cdots + 90 = {10over2}(0 + 90)= 5cdot 90 = 450$$
Addendum:
If you know the first element ($a_1$), number of elements ($n$) and their sum ($s$), you may obtain the last element ($a_n$) by substituting the known values into the formula, and then isolate $a_n$:
$$a_n = {2sover n}-a_1$$
You may then compute the difference $d$ between adjacent members as
$$d = {a_n-a_1over n-1}$$
to consecutively obtain members between $a_1$ and $a_n$:
begin{aligned}
a_2 &= a_1+d\a_3 &= a_2+d\
&cdots
end{aligned}
(To the question in your comment.)
edited Mar 25 at 5:24
answered Mar 25 at 4:37
MarianDMarianD
1,7791617
1,7791617
$begingroup$
Using this approach it appears I need to know the answer toan
(90) - if I only havea1
(0) and 450, could it still be done?
$endgroup$
– Ryan Gillies
Mar 25 at 4:43
$begingroup$
@Ryan You have the values for n, $a_1$, and the sum. That leaves $a_n$ as the only variable. You can solve for $a_n$ to get $a_n=frac{2}{n}(x)-a_1$ where $x$ is the sum (450 in your case).
$endgroup$
– Jacob Jones
Mar 25 at 4:57
$begingroup$
Sorry yes you're right I forgot to include that in my comment, I will always know number of elements (n) first number in sequence (a1) and the sum (in this example 450). What I don't know is the last number in sequence (an).
$endgroup$
– Ryan Gillies
Mar 25 at 4:57
$begingroup$
You need know also the number of elements ($n$) to substitute it to the given formula, because without this you may write the sum $450$ in many different ways, e. g. $450 = 0 + 450 = 0 + 150 + 300 = 0 +45 +90 +135 +180$.
$endgroup$
– MarianD
Mar 25 at 5:00
$begingroup$
Nailed it, understood perfectly! Thank you so much for your help MarianD and @JacobJones!
$endgroup$
– Ryan Gillies
Mar 25 at 5:01
add a comment |
$begingroup$
Using this approach it appears I need to know the answer toan
(90) - if I only havea1
(0) and 450, could it still be done?
$endgroup$
– Ryan Gillies
Mar 25 at 4:43
$begingroup$
@Ryan You have the values for n, $a_1$, and the sum. That leaves $a_n$ as the only variable. You can solve for $a_n$ to get $a_n=frac{2}{n}(x)-a_1$ where $x$ is the sum (450 in your case).
$endgroup$
– Jacob Jones
Mar 25 at 4:57
$begingroup$
Sorry yes you're right I forgot to include that in my comment, I will always know number of elements (n) first number in sequence (a1) and the sum (in this example 450). What I don't know is the last number in sequence (an).
$endgroup$
– Ryan Gillies
Mar 25 at 4:57
$begingroup$
You need know also the number of elements ($n$) to substitute it to the given formula, because without this you may write the sum $450$ in many different ways, e. g. $450 = 0 + 450 = 0 + 150 + 300 = 0 +45 +90 +135 +180$.
$endgroup$
– MarianD
Mar 25 at 5:00
$begingroup$
Nailed it, understood perfectly! Thank you so much for your help MarianD and @JacobJones!
$endgroup$
– Ryan Gillies
Mar 25 at 5:01
$begingroup$
Using this approach it appears I need to know the answer to
an
(90) - if I only have a1
(0) and 450, could it still be done?$endgroup$
– Ryan Gillies
Mar 25 at 4:43
$begingroup$
Using this approach it appears I need to know the answer to
an
(90) - if I only have a1
(0) and 450, could it still be done?$endgroup$
– Ryan Gillies
Mar 25 at 4:43
$begingroup$
@Ryan You have the values for n, $a_1$, and the sum. That leaves $a_n$ as the only variable. You can solve for $a_n$ to get $a_n=frac{2}{n}(x)-a_1$ where $x$ is the sum (450 in your case).
$endgroup$
– Jacob Jones
Mar 25 at 4:57
$begingroup$
@Ryan You have the values for n, $a_1$, and the sum. That leaves $a_n$ as the only variable. You can solve for $a_n$ to get $a_n=frac{2}{n}(x)-a_1$ where $x$ is the sum (450 in your case).
$endgroup$
– Jacob Jones
Mar 25 at 4:57
$begingroup$
Sorry yes you're right I forgot to include that in my comment, I will always know number of elements (n) first number in sequence (a1) and the sum (in this example 450). What I don't know is the last number in sequence (an).
$endgroup$
– Ryan Gillies
Mar 25 at 4:57
$begingroup$
Sorry yes you're right I forgot to include that in my comment, I will always know number of elements (n) first number in sequence (a1) and the sum (in this example 450). What I don't know is the last number in sequence (an).
$endgroup$
– Ryan Gillies
Mar 25 at 4:57
$begingroup$
You need know also the number of elements ($n$) to substitute it to the given formula, because without this you may write the sum $450$ in many different ways, e. g. $450 = 0 + 450 = 0 + 150 + 300 = 0 +45 +90 +135 +180$.
$endgroup$
– MarianD
Mar 25 at 5:00
$begingroup$
You need know also the number of elements ($n$) to substitute it to the given formula, because without this you may write the sum $450$ in many different ways, e. g. $450 = 0 + 450 = 0 + 150 + 300 = 0 +45 +90 +135 +180$.
$endgroup$
– MarianD
Mar 25 at 5:00
$begingroup$
Nailed it, understood perfectly! Thank you so much for your help MarianD and @JacobJones!
$endgroup$
– Ryan Gillies
Mar 25 at 5:01
$begingroup$
Nailed it, understood perfectly! Thank you so much for your help MarianD and @JacobJones!
$endgroup$
– Ryan Gillies
Mar 25 at 5:01
add a comment |
$begingroup$
$$sumlimits_{i=0}^9 10 i = 10 sumlimits_{i=0}^9 i = 10 left[ frac{(9+0)(9+1)}{2} right] =450$$
$endgroup$
add a comment |
$begingroup$
$$sumlimits_{i=0}^9 10 i = 10 sumlimits_{i=0}^9 i = 10 left[ frac{(9+0)(9+1)}{2} right] =450$$
$endgroup$
add a comment |
$begingroup$
$$sumlimits_{i=0}^9 10 i = 10 sumlimits_{i=0}^9 i = 10 left[ frac{(9+0)(9+1)}{2} right] =450$$
$endgroup$
$$sumlimits_{i=0}^9 10 i = 10 sumlimits_{i=0}^9 i = 10 left[ frac{(9+0)(9+1)}{2} right] =450$$
answered Mar 25 at 4:34
David G. StorkDavid G. Stork
11.5k41533
11.5k41533
add a comment |
add a comment |
Ryan Gillies is a new contributor. Be nice, and check out our Code of Conduct.
Ryan Gillies is a new contributor. Be nice, and check out our Code of Conduct.
Ryan Gillies is a new contributor. Be nice, and check out our Code of Conduct.
Ryan Gillies is a new contributor. Be nice, and check out our Code of Conduct.
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$begingroup$
The keywords you need are "arithmetic progression".
$endgroup$
– FredH
Mar 25 at 4:33
$begingroup$
Thank you, that instantly helps a lot with my googling!
$endgroup$
– Ryan Gillies
Mar 25 at 4:39