Question

Find the indicated sum. Select your choice and click Submit to check your answer.

Answer 1

Answer:

$S_4=50$

Step-by-step explanation:

Sum Of Arithmetic Sequence

Given an arithmetic sequence

$a_1,\ a_1+r,\ a_1+2r,....,\ a_1+(n-1)r$

The sum of the n first terms is

$\displaystyle S_n=\frac{(a_1+a_n)n}{2}$

Or equivalently

$\displaystyle S_n=\frac{[2a_1+(n-1)r]n}{2}$

The given sequence is

5, 8, 11 ...

We can see the common difference between terms is r=3

We are asked to find the sum of the terms 2 to 5, it means that

$a_1=8, n=4, r=3$

$\displaystyle S_4=\frac{[2(8)+(4-1)3]4}{2}$

$\displaystyle S_4=\frac{100}{2}$

$\boxed{S_4=50}$