Question

If a679b is a five digit number that is divisible by 72 determine a+b.

Answer 1

$a679b$ is divided by $72$

$\Rightarrow a679b$ is divided by $8\&9$

As $a6796$ is divided by $8$

$\Rightarrow 79b$ is divided by $8$

$\Rightarrow b=2$ $(\because 792/8=99)$

$\Rightarrow$ for divisible by ${}^{\prime }{9}^{\prime }a+6+7+9+2$

is divided by $9\therefore a=3\Rightarrow a+b=5$