Question

I am an even number. The sum of the digits is divisible by 9. I am also a multiple of 15, but I am less than 100. Who am I?

Answer 1

An even number is a multiple of $2.$
The sum of the digits is divisible by $9.$
$\therefore$ It must be a multiple of $9.$

Also, it is a multiple of $15.$
$15=3\times 5$
$\therefore$ It must also be a multiple of $5.$

$2\times 9\times 5=90$
Also, $90$ is less than $100.$

$\therefore 90$ is the required answer.