Question

find 20th term from the last term of an ap 3, 8 ,13,...... 253

Answer 1

A1 = 3
A2 = 8
l = 253

Common difference(d) = A2 - A1 = 8 - 3 = 5

To find 20th term from last we use

A20 = l - (20 -1)d

A20 = 253 - 19 × 5

A20 = 253 - 95

A20 = 158

Ans. 20th term from last is 158

Answer 2

Solution :

We have, l = Last term = 253

and,

               d = Common difference = 8 - 3 = 5

∴ 20th term from the end = l - (20 - 1)d

                                           = l - 19d

                                           = 253 - 19 × 5

                                           = 253 - 95 = 158