Find the smallest square number that is divisible by each of the numbers $8,15and20$.

Let us find LCM of $8,15$ and $20$
$8=2\times 2\times 2$
$15=3\times 5$
$20=2\times 2\times 5$
So, LCM $=2\times 2\times 2\times 3\times 5=120$.
For nos which are not in pairs in LCM factors, we need to multiply $120$ by $2$, $3$ and $5$ to make it a perfect square.
Required Number $=120\times 2\times 3\times 5=3600$