Question

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

A. 162
B. 151
C. 157
D. 154

Answer 1

a 1 = 13,  d = 3;
S n = n/2 * ( a 1 + a n )
a 7 = a 1 + 6 d = 13 + 3 * 6 = 13 + 18 = 31
S 7 = 7/2 * ( 13 + 31 ) = 7/2 * 44 = 154
Answer:
D ) 154 

Answer 2

Answer:

The correct option is D.

Step-by-step explanation:

The first term of an AP is $a_1=13$.

The common difference of AP is 3.

The sum of nth term of an AP is

$S_n=\frac{n}{2}[2a+(n-1)d]$

Where, a is first term and d is common difference.

We have to find S₇.

$S_7=\frac{7}{2}[2(13)+(7-1)3]$

$S_7=\frac{7}{2}[26+18]$

$S_7=\frac{7}{2}(44)$

$S_7=7\times 22$

$S_7=154$

Therefore the correct option is D.