Find the sum of a 24–term arithmetic sequence where the first term is 12 and the last term is 219

Harrison Mills
2022-09-23
Answered

Find the sum of a 24–term arithmetic sequence where the first term is 12 and the last term is 219

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ruinsraidy4

Answered 2022-09-24
Author has **17** answers

What you are actually doing (in your mind or on paper) is putting the sequence in a row and beneath that you put the same sequence in reverse order. Now when you add them vertically, two by two, you will get the same number (=first+last) every time:

Example :

1 2 3 4 5

5 4 3 2 1 +

6 6 6 6 6

This will be 6 x 5 = 30, because there are 5 terms here. But now you have added two sequences, so you have to divide by 2.

In your case: $Sum=\frac{(12+219)\cdot 24}{2}$

Example :

1 2 3 4 5

5 4 3 2 1 +

6 6 6 6 6

This will be 6 x 5 = 30, because there are 5 terms here. But now you have added two sequences, so you have to divide by 2.

In your case: $Sum=\frac{(12+219)\cdot 24}{2}$

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