Question

For an arithmetic sequence where a1 = 13 and the common difference is 3, find s7.

Answer 1

Sn=n/2[2a+(n-1)d]
s7 means n=7

a7=7/2[2(13)+(7-1)(3)]=7/2(44)=154

Ans:C

Answer 2

Answer:

C. 154

Step-by-step explanation:

Here we have given that,

First Term a₁ = 13

Common Difference d = 3

Term (n ) = 7

so, we have arithmetic sequence: 13, 16, 19, 22,... and so on

Thus Sum of first 7 terms = $\frac{n}{2} [2a+(n-1)d]$

                                          = 7÷2 [2*13 + (7 - 1)*3 ]

                                          = 3.5 [ 26 + 21 ]

                                          = 154