Question

Find the 20^th term from the last term of the A.P. 3, 8, 13, …, 253.

Answer 1

Given A.P. is

3, 8, 13, …, 253

Common difference for this A.P. is 5.

Therefore, this A.P. can be written in reverse order as

253, 248, 243, …, 13, 8, 3

For this A.P.,

a = 253

d = 248 − 253

d = −5

n = 20

a₂₀ = a + (20 − 1) d

a₂₀ = 253 + (19) (−5)

a₂₀ = 253 − 95

a = 158

Therefore, 20^th term from the last term is 158.