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 60 minutes? Choices
A) 80  B) 100  C) 150  D) 240  E) 300

Rationale: "since the population increases at the rate of 1 person every 15 seconds , it increases by 4 people every 60 seconds , that is , by 4 people every minute . thus , in 60 minutes the population increases by 60 x 4 = 240 people . answer . d ."
Answer: D