Q13 of 178 Page 559

An AP 5, 12, 19, ... has 50 terms. Its last term is

Here, first term = 5

Common difference = 12 - 5 = 7

Given that there are 50 terms in the AP.

To find: Last term, i.e. 50^th term = a₅₀

Since a_n = a + (n - 1)d

∴ a₅₀ = 5 + (50 - 1)7

= 5 + (49) × 7

= 5 + 343

= 348

The 5th term of an AP is 20 and the sum of its 7th and 11th terms is 64. The common difference of the AP is

The 13th term of an AP is 4 times its 3rd term. If its 5th term is 16 then the sum of its first ten terms is

The sum of first 20 odd natural numbers is

The sum of first 40 positive integers divisible by 6 is