Question

if the sum of first 13 term is 91 and the sum of the first 30 term is 465 find the sum of its first 50 terms

Answer 1

Here the sum of 13 terms is 91.

This means. a + 12d = 91

and a + 29 d = 465

Subtracting the above equations we get,
17 d = 374
d= 22

Putting value of d in the first equation, we get a= -173

Now sum of 50 terms = a +49 d = 814