#### Answer

80

#### Work Step by Step

First, we express each number as a product of prime factors:
$16=2\times2\times2\times2$
$20=2\times2\times5$
$80=2\times2\times2\times2\times5$
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 four times.
The most times 5 appears is once.
LCM$=2\times2\times2\times2\times5=80$