Question

Let $\ast$ be the binary operation on $N$ given by $a\ast b=$ LCM of $a$ and $b$. Find
$5\ast 7$ $20\ast 16$

Answer 1

$20\times 16$ = LCM of $20$ and $16$

For finding out the LCM multiply each factor the greatest number of times it occurs in any of the numbers.

$20=2\times 2\times 5$

$16=2\times 2\times 2\times 2$

Max number of times 2 occurs $=4$

Max number of times 5 occurs $=1$

$LCM=16=2\times 2\times 2\times 2\times 5=320$

Hence the answer is $320.$