An arithmetic progression is simply a progression with a common difference among consecutive terms.
- <em>The sum of multiplies of 6 between 8 and 70 is 390</em>
- <em>The sum of multiplies of 5 between 12 and 92 is 840</em>
- <em>The sum of multiplies of 3 between 1 and 50 is 408</em>
- <em>The sum of multiplies of 11 between 10 and 122 is 726</em>
- <em>The sum of multiplies of 9 between 25 and 100 is 567</em>
- <em>The sum of the first 20 terms is 630</em>
- <em>The sum of the first 15 terms is 480</em>
- <em>The sum of the first 32 terms is 3136</em>
- <em>The sum of the first 27 terms is -486</em>
- <em>The sum of the first 51 terms is 2193</em>
<em />
<u>(a) Sum of multiples of 6, between 8 and 70</u>
There are 10 multiples of 6 between 8 and 70, and the first of them is 12.
This means that:
![\mathbf{a = 12}](https://tex.z-dn.net/?f=%5Cmathbf%7Ba%20%3D%2012%7D)
![\mathbf{n = 10}](https://tex.z-dn.net/?f=%5Cmathbf%7Bn%20%3D%2010%7D)
![\mathbf{d = 6}](https://tex.z-dn.net/?f=%5Cmathbf%7Bd%20%3D%206%7D)
The sum of n terms of an AP is:
![\mathbf{S_n = \frac n2(2a + (n - 1)d)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_n%20%3D%20%5Cfrac%20n2%282a%20%2B%20%28n%20-%201%29d%29%7D)
Substitute known values
![\mathbf{S_{10} = \frac{10}2(2*12 + (10 - 1)6)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B10%7D%20%3D%20%5Cfrac%7B10%7D2%282%2A12%20%2B%20%2810%20-%201%296%29%7D)
![\mathbf{S_{10} = 390}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B10%7D%20%3D%20390%7D)
<u>(b) Multiples of 5 between 12 and 92</u>
There are 16 multiples of 5 between 12 and 92, and the first of them is 15.
This means that:
![\mathbf{a = 15}](https://tex.z-dn.net/?f=%5Cmathbf%7Ba%20%3D%2015%7D)
![\mathbf{n = 16}](https://tex.z-dn.net/?f=%5Cmathbf%7Bn%20%3D%2016%7D)
![\mathbf{d = 5}](https://tex.z-dn.net/?f=%5Cmathbf%7Bd%20%3D%205%7D)
The sum of n terms of an AP is:
![\mathbf{S_n = \frac n2(2a + (n - 1)d)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_n%20%3D%20%5Cfrac%20n2%282a%20%2B%20%28n%20-%201%29d%29%7D)
Substitute known values
![\mathbf{S_{16} = \frac{16}2(2*15 + (16 - 1)5)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B16%7D%20%3D%20%5Cfrac%7B16%7D2%282%2A15%20%2B%20%2816%20-%201%295%29%7D)
![\mathbf{S_{16} = 840}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B16%7D%20%3D%20840%7D)
<u>(c) Multiples of 3 between 1 and 50</u>
There are 16 multiples of 3 between 1 and 50, and the first of them is 3.
This means that:
![\mathbf{a = 3}](https://tex.z-dn.net/?f=%5Cmathbf%7Ba%20%3D%203%7D)
![\mathbf{n = 16}](https://tex.z-dn.net/?f=%5Cmathbf%7Bn%20%3D%2016%7D)
![\mathbf{d = 3}](https://tex.z-dn.net/?f=%5Cmathbf%7Bd%20%3D%203%7D)
The sum of n terms of an AP is:
![\mathbf{S_n = \frac n2(2a + (n - 1)d)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_n%20%3D%20%5Cfrac%20n2%282a%20%2B%20%28n%20-%201%29d%29%7D)
Substitute known values
![\mathbf{S_{16} = \frac{16}2(2*3 + (16 - 1)3)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B16%7D%20%3D%20%5Cfrac%7B16%7D2%282%2A3%20%2B%20%2816%20-%201%293%29%7D)
![\mathbf{S_{16} = 408}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B16%7D%20%3D%20408%7D)
<u>(d) Multiples of 11 between 10 and 122</u>
There are 11 multiples of 11 between 10 and 122, and the first of them is 11.
This means that:
![\mathbf{a = 11}](https://tex.z-dn.net/?f=%5Cmathbf%7Ba%20%3D%2011%7D)
![\mathbf{n = 11}](https://tex.z-dn.net/?f=%5Cmathbf%7Bn%20%3D%2011%7D)
![\mathbf{d = 11}](https://tex.z-dn.net/?f=%5Cmathbf%7Bd%20%3D%2011%7D)
The sum of n terms of an AP is:
![\mathbf{S_n = \frac n2(2a + (n - 1)d)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_n%20%3D%20%5Cfrac%20n2%282a%20%2B%20%28n%20-%201%29d%29%7D)
Substitute known values
![\mathbf{S_{16} = \frac{11}2(2*11 + (11 - 1)11)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B16%7D%20%3D%20%5Cfrac%7B11%7D2%282%2A11%20%2B%20%2811%20-%201%2911%29%7D)
![\mathbf{S_{11} = 726}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B11%7D%20%3D%20726%7D)
<u />
<u>(e) Multiples of 9 between 25 and 100</u>
There are 9 multiples of 9 between 25 and 100, and the first of them is 27.
This means that:
![\mathbf{a = 27}](https://tex.z-dn.net/?f=%5Cmathbf%7Ba%20%3D%2027%7D)
![\mathbf{n = 9}](https://tex.z-dn.net/?f=%5Cmathbf%7Bn%20%3D%209%7D)
![\mathbf{d = 9}](https://tex.z-dn.net/?f=%5Cmathbf%7Bd%20%3D%209%7D)
The sum of n terms of an AP is:
![\mathbf{S_n = \frac n2(2a + (n - 1)d)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_n%20%3D%20%5Cfrac%20n2%282a%20%2B%20%28n%20-%201%29d%29%7D)
Substitute known values
![\mathbf{S_{9} = \frac{9}2(2*27 + (9 - 1)9)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B9%7D%20%3D%20%5Cfrac%7B9%7D2%282%2A27%20%2B%20%289%20-%201%299%29%7D)
![\mathbf{S_{9} = 567}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B9%7D%20%3D%20567%7D)
<u>(f) Sum of first 20 terms</u>
The given parameters are:
![\mathbf{a = 3}](https://tex.z-dn.net/?f=%5Cmathbf%7Ba%20%3D%203%7D)
![\mathbf{d = 3}](https://tex.z-dn.net/?f=%5Cmathbf%7Bd%20%3D%203%7D)
![\mathbf{n = 20}](https://tex.z-dn.net/?f=%5Cmathbf%7Bn%20%3D%2020%7D)
The sum of n terms of an AP is:
![\mathbf{S_n = \frac n2(2a + (n - 1)d)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_n%20%3D%20%5Cfrac%20n2%282a%20%2B%20%28n%20-%201%29d%29%7D)
Substitute known values
![\mathbf{S_{20} = \frac{20}2(2*3 + (20 - 1)3)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B20%7D%20%3D%20%5Cfrac%7B20%7D2%282%2A3%20%2B%20%2820%20-%201%293%29%7D)
![\mathbf{S_{20} = 630}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B20%7D%20%3D%20630%7D)
<u>(f) Sum of first 15 terms</u>
The given parameters are:
![\mathbf{a = 4}](https://tex.z-dn.net/?f=%5Cmathbf%7Ba%20%3D%204%7D)
![\mathbf{d = 4}](https://tex.z-dn.net/?f=%5Cmathbf%7Bd%20%3D%204%7D)
![\mathbf{n = 15}](https://tex.z-dn.net/?f=%5Cmathbf%7Bn%20%3D%2015%7D)
The sum of n terms of an AP is:
![\mathbf{S_n = \frac n2(2a + (n - 1)d)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_n%20%3D%20%5Cfrac%20n2%282a%20%2B%20%28n%20-%201%29d%29%7D)
Substitute known values
![\mathbf{S_{15} = \frac{15}2(2*4 + (15 - 1)4)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B15%7D%20%3D%20%5Cfrac%7B15%7D2%282%2A4%20%2B%20%2815%20-%201%294%29%7D)
![\mathbf{S_{15} = 480}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B15%7D%20%3D%20480%7D)
<u>(g) Sum of first 32 terms</u>
The given parameters are:
![\mathbf{a = 5}](https://tex.z-dn.net/?f=%5Cmathbf%7Ba%20%3D%205%7D)
![\mathbf{d = 6}](https://tex.z-dn.net/?f=%5Cmathbf%7Bd%20%3D%206%7D)
![\mathbf{n = 32}](https://tex.z-dn.net/?f=%5Cmathbf%7Bn%20%3D%2032%7D)
The sum of n terms of an AP is:
![\mathbf{S_n = \frac n2(2a + (n - 1)d)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_n%20%3D%20%5Cfrac%20n2%282a%20%2B%20%28n%20-%201%29d%29%7D)
Substitute known values
![\mathbf{S_{32} = \frac{32}2(2*5 + (32 - 1)6)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B32%7D%20%3D%20%5Cfrac%7B32%7D2%282%2A5%20%2B%20%2832%20-%201%296%29%7D)
![\mathbf{S_{32} = 3136}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B32%7D%20%3D%203136%7D)
<u>(g) Sum of first 27 terms</u>
The given parameters are:
![\mathbf{a = 8}](https://tex.z-dn.net/?f=%5Cmathbf%7Ba%20%3D%208%7D)
![\mathbf{d = -2}](https://tex.z-dn.net/?f=%5Cmathbf%7Bd%20%3D%20-2%7D)
![\mathbf{n = 27}](https://tex.z-dn.net/?f=%5Cmathbf%7Bn%20%3D%2027%7D)
The sum of n terms of an AP is:
![\mathbf{S_n = \frac n2(2a + (n - 1)d)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_n%20%3D%20%5Cfrac%20n2%282a%20%2B%20%28n%20-%201%29d%29%7D)
Substitute known values
![\mathbf{S_{27} = \frac{27}2(2*8 + (27 - 1)*-2)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B27%7D%20%3D%20%5Cfrac%7B27%7D2%282%2A8%20%2B%20%2827%20-%201%29%2A-2%29%7D)
![\mathbf{S_{27} = -486}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B27%7D%20%3D%20-486%7D)
<u>(h) Sum of first 51 terms</u>
The given parameters are:
![\mathbf{a = -7}](https://tex.z-dn.net/?f=%5Cmathbf%7Ba%20%3D%20-7%7D)
![\mathbf{d = 2}](https://tex.z-dn.net/?f=%5Cmathbf%7Bd%20%3D%202%7D)
![\mathbf{n = 51}](https://tex.z-dn.net/?f=%5Cmathbf%7Bn%20%3D%2051%7D)
The sum of n terms of an AP is:
![\mathbf{S_n = \frac n2(2a + (n - 1)d)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_n%20%3D%20%5Cfrac%20n2%282a%20%2B%20%28n%20-%201%29d%29%7D)
Substitute known values
![\mathbf{S_{51} = \frac{51}2(2*-7 + (51 - 1)*2)}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B51%7D%20%3D%20%5Cfrac%7B51%7D2%282%2A-7%20%2B%20%2851%20-%201%29%2A2%29%7D)
![\mathbf{S_{51} = 2193}](https://tex.z-dn.net/?f=%5Cmathbf%7BS_%7B51%7D%20%3D%202193%7D)
Read more about arithmetic progressions at:
brainly.com/question/13989292