Find the sum of 20th and 25th terms of A.P. 2, 5, 8, 11, ...

Given: 2, 5, 8, 11, …

Here, a = 2

d = a₂ – a₁ = 5 – 2 = 3

and n = 20

We have,

t_n = a + (n – 1)d

t₂₀ = 2 + (20 – 1)(3)

t₂₀ = 2 + 19 × 3

= 2 + 57

t₂₀ = 59

Now, n = 25

t₂₅ = 2 + (25 – 1)(3)

t₂₅ = 2 + 24 × 3

t₂₅ = 2 + 72

t₂₅ = 74

The sum of 20^th and 25^th terms of AP = t₂₀ + t₂₅ = 59 + 74 = 133