I believe the solution should be:

(20*60)/15 = 80

Option A

Population increases at the rate of 1 person every 15 seconds = Population increase at the rate of 4 persons per minute
so in 20 minutes the population will increase by 20*4 = 80

so the answer is A

islands80 wrote:If the population of a certain country increases at the rate of one person every 15 seconds, by how many persons does the population increase in 20 minutes?

(A) 80
(B) 100
(C) 150
(D) 240
(E) 300

We are given that a population increases by 1 person every 15 seconds and we need to determine how many people it will increase by in 20 minutes, which is 20 x 60 = 1200 seconds. We can let x = the number of people increased in 20 minutes and create the following proportion:

1/15 = x/1200

15x = 1200

x = 80

Alternate Solution:

One person every 15 seconds equals 4 people per minute. Thus, in 20 minutes, we have 4 x 20 = 80 people.

Answer: A