Question

Between 1965 and 1980, the world population grew at an annual rate of 2%. Using the rule of 72, population is expected to double in

Select one:

a. 144 years.

b. 36 years.

c. 24 years.

d. 18 years.

Answer 1

The rule of 72 states that in order to find out in how many years, our investment would double up, given that we know the interest rate at which the investment grows, then we can divide 72 by the interest rate to determine the number of years it would take for our investment to double up. For example, if we know that the rate at which investment grows is 4% and we need to know in how many years our investment will become double, we just divide 74 by 4 and the answer (here: 18 ) is the number of years needed to double up our investment.

                                                     If we apply the same rule in this given case, then the total number of years needed for the population to become double will be :                                                                      

$=\frac{72}{2}$

$=36$

Therefore the correct answer is b.36 years.