Question

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

Answer 1

Solution: a = 3, d = 5

Now, 253 = a + (n + 1) d

⇒ 253 = 3 + (n -1) x 5

⇒ 253 = 3 + 5n – 5 = – 2

⇒ 5n = 253 + 2 = 255

⇒ n = 255/5 = 51

Therefore, 20th term from the last term = 51 – 19 = 32

a32 = a + 31d

= 3 + 31 x 5

= 3 + 155 = 158

Thus, required term is 158