Answer :

m=3L
m+L=24
3L+L=24
4L=24
L=6
m=3L
m=3(6)
There are 18 monkeys.
Good morning, 

L= number of lions at the zoo
M= number of monkeys at the zoo, but we know that there were 3 times as many monkeys as lios, so:  [tex]M=3L-->L= \frac{M}{3} [/tex]

Tom counted a total of 24 monkeys and lions, so:

[tex]M+L=24 \\ \\ M+ \frac{M}{3} =24 \\ \\ \frac{4}{3}M=24 \\ \\ M= \frac{24*3}{4} \\ \\ M=18[/tex]

Answer: There were 18 monkeys