Q. 45.0( 1 Vote )

# 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,

tn = 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 20th and 25th terms of AP = t20 + t25 = 59 + 74 = 133

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