Answer:
USING RULE OF 70
Number of years to double = 70 ÷ annual percentage growth rate.
Therefore,
1. Number of years it will take South Africa to double its GDP = 70 ÷ 1.8
= 38.89
= 39 years
2. Average per capital growth rate of Ireland GDP = 70 ÷ No. Of years to double
=70 ÷ 15
= 4.67 %
3. Time it will take Tanzania to quadruple their GDP = (70 ÷ 0.8) × 2
= 87.5 × 2
= 175 years.
NOTE. We multiplied it by 2 because the question was quadruple not double.
4. Average economic growth of China during this period = (70 ÷ 40) × 3
= 1.75 × 3
= 5.25 %
Note - Rule of 70 is a method used in estimating an investment doubling time. We also have Rule of 72 and rule of 69.