Question

Find the sum of 15 terms of an A.P whose middle term is – 42

Answer 1

Step-by-step explanation:

Given middle term or the sixth term is 30

As we know, a

n

=a+(n−1)d, where a & d are the first term and common difference of an AP respectively.

Then, a+5d=30

Sum =

2

n

(2a+(n−1)d)

=

2

11

(2a+10d)

Substituting,

=

2

11

(2×30)

=330