How many natural numbers are there between 23 and 100 which are exactly divisible by 6 ?

Required numbers are 24, 30, 36, 42, ..., 96

This is an A.P. in which a = 24, d = 6 and l = 96

Let the number of terms in it be n.

Then t_n = 96    a + (n - 1)d = 96

 24 + (n - 1) x 6 = 96

 (n - 1) x 6 = 72

 (n - 1) = 12

 n = 13

Required number of numbers = 13.