Question

Which term of the sequence 3, 8, 13, ........ is 78?

Answer 1

The given sequence is 3, 8, 13, ........

Now,

8 – 3 = 13 – 8 = 5

Hence, the given sequence is an A.P. with first term a = 3 and common difference d = 5.

Let the n^th term of the given A.P. be 78.

⇒ 78 = 3 + (n – 1)(5)

⇒ 75 = 5n – 5

⇒ 5n = 80

⇒ n = 16

Thus, the 16^th term of the given sequence is 78.