Question

How many 2 digits numbers are divisible by 9?

Answer 1

Multiples of 9

9, 18, 27, 36, 45, 54, 63,...99...

According to the problem we want only two digit numbers which are divisble by 9

$18,27,36,45,54,63,...99.$

$\therefore$ $a=18,d=9,a_n=99$

Substituting $a,d,a_n$ in general term

$a_n=a+(n-1)d$

$99=18+(n-1)9$

$81=(n-1)9$

$n-1=9$

$n=10$

So, there are ten $2$ digits numbers which are divisible by $9$