Answer:
Ratio defined as the comparison between two sizes or number.
i.,e a to b = a: b or

As per the statement:
comparing the first quantity to the second quantity a zoo has 19 monkeys and 10 chimpanzees.
First quantity = 19 monkeys
Second quantity = 10 chimpanzees.
then by definition of ratio:

We have to find the ratio for the situation in three ways.
Ratios for the situation in three ways;
19 to 10

19:10