Question

The total number of six digit numbers, formed using the digits $4,5,9$ only and divisible by 6 , is __

Answer 1

Answer: 81

Taking three digit
$4,5,9,4,4,4\Rightarrow \frac{5!}{3!}=20$
$4,5,9,5,5,5\Rightarrow \frac{5!}{4!}=5$
$4,5,9,9,9,9\Rightarrow \frac{5!}{4!}=5$
$4,5,9,4,5,9\Rightarrow \frac{5!}{2!2!}=30$
$\text{ Total }=81$