Question

FIND THE 20 TH TERM FROM THE LAST TERM OF THE AP: 3,8,13,.......253.

Answer 1

Here, we have a=3, d=8-3=5, l=253

First we have to calculate, number (n) of series:

 l=a+(n-1)d

253=3+(n-1)5

250=5n-5

255/5=n

n=51

You have to calculate 20th term from last, if you will notice then it would be 32(don't forget to including 51):

a32 = a+(n-1)d   where n=32

= 3+(31)5

=3+155

=158 ANS

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