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 tn = 96 $\Rightarrow$ $ a $ + $\left(n - 1\right)$d = 96
$\Rightarrow$ 24 + $\left( n - 1\right)$ x 6 = 96
$\Rightarrow$ $\left( n - 1\right)$ x 6 = 72
$\Rightarrow$ $\left( n - 1\right)$ = 12
$\Rightarrow n $ = 13
Required number of numbers = 13.