Integrate cos(2theta)d(theta) from 0 to pi/5

50 deer in the forest.

Step-by-step explanation:

Since this is a ratio problem and we are given three values and a single unknown (total number of deer) we can use the Rule of three to solve for the variable. We do this by multiplying the diagonal values and then dividing by the last available value. That will give us the value of the variable which in this case would be represented as x.

20 deer <>  6 tagged

x  deer  <>  15 tagged

(20*15) / 6 = x

300 / 6 = 50 total deer

Based on these values we can estimate that there are a total of 50 deer in the forest.