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?
সঠিক উত্তর: Option A
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 20 minutes the population increases by 20 x 4 = 80 people.