Question

A zookeeper thinks there is a problem with the naked-mole rat population at the zoo. He starts keeping track of the animals in the tunnels. 7 days into his monitoring he counts 120 mole rats. 13 days in he counts 108. How many rats where there when he started monitoring?.

Answer 1

17 naked mole rats.....

Answer 2

The rat population at the zoo when the zookeeper starts counting can be found to be 134 .

How to find the initial population?

In 7 days, he counts 120 mole rats, so the rate at which the population is decreasing is (x - 120)/7.

In 13 days, he counts 108 mole rats, so the rate at which the population is decreasing is (x - 108)/13.

Now, set up the proportion:

(x - 120)/7 = (x - 108)/13

13(x - 120) = 7(x - 108)

13x - 1560 = 7x - 756

6x - 1560 = -756

6x = 804

x = 804 / 6

x = 134

There were initially 134 mole rats when the zookeeper started monitoring.