Question

How many numbers of two digits are divisible by 5?

Answer 1

Two-digit numbers divisible by 5 are 10, 15, 20, ..., 95.

Here, d = 5, this sequence is an A.P.

Here, a = 10, d = 5, t_n = 95, n = ?

t_n = a + (n − 1) d

 ∴ 95 = 10 + (n – 1) × 5

∴ 95 – 10 = (n – 1) × 5

∴ 85 = (n – 1) × 5

∴ `85/5` = (n – 1)

∴ 17 = (n – 1)

∴ n = 17 + 1

Therefore n = 18

There are 18 two-digit numbers divisible by 5.