Question

The sum of first 10 terms of an AP is -150 and the sum of its next 10 terms is -550. Find the AP.

Answer 1

Let a be the first term and d be the common difference of the AP.

Then,

It is given that the sum of its next 10 terms is – 550

Now

$S_{20}$ = Sum of first 20 terms = Sum of first 10 terms + Sum of the next 10 terms = – 150 + (- 550 ) = -700

Subtracting (i) from (ii), we get


Putting d = -4 in (i), we get