Question

Mark the correct alternative in each of the following:

If 7th and 13th terms of an A.P. be 34 and 64 respectively, then its 18th term is

(a) 87

(b) 88

(c) 89

(d) 90

Answer 1

In the given problem, we are given 7^th and 13^th term of an A.P.

We need to find the 26^th term

Here,

Now, we will find and using the formula

So,

Also,

Further, to solve for a and d

On subtracting (1) from (2), we get

Substituting (3) in (1), we get

Thus,

So, for 18^th term (n = 18),

Substituting the above values in the formula,

Therefore,

Hence, the correct option is (c).