Question

Find a and b so that the following odd numbers are divisible by both 3 and 5:
(i)7b25 (ii) 8ab4b

Answer 1

$\left(i\right)7b25$

It is divisible by 5.

For it to be divisible by 3, $5+b$ must be divisible by 3.

Therefore, $b=1,4,7$

$\left(ii\right)8ab4b$

For the number to be odd and divisible by 5, $b=5$

Now, for it to be divisible by 3, $4+a$ must be divisible by 3.

Therefore, $a=2,5,8$