Answer
200
Work Step by Step
First, we express each number as a product of prime factors:
$40=2\times2\times2\times5$
$100=2\times2\times5\times5$
The least common multiple includes each different prime factor as many times as the most times it appears in one of the factorizations.
The most times 2 appears is three times
The most times 5 appears is twice.
LCM$=2\times2\times2\times5\times5=200$
