Question

find the 20th term from the last term of the AP:3,8,13,....,253

Answer 1

In the new A.P. first term a = 253 and common difference d = 3 – 8 = –5

We know that

an = a + (n – 1) d

⇒ a20 = 253 + (20 – 1) (–5)

= 253 + 19 × (–5)

= 253 – 95 = 158



Hence 20th term from the last of the A.P. 3, 8, 13 ... 253 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