Assuming a country's economy maintains an 8% rate of growth, young adults starting at age 20 would see the average standard of living in their country more than double by the time they had reached age .

A. 30
B. 40
C. 50
D. 60

A) 30

Explanation:

to determine in how many years the economy will double with an 8% growth rate, we can use the rule of 72. The rule of 72 basically works by dividing 72 by the compounding growth rate to determine the number of years it will take an investment to double.

The rule of 72 works well when growth rate is between 6-10%, at 8% it is quite exact. For lower growth rates you should use the rule of 70 which is basically the same but instead of using 72, you use 70. For growth rates over 10% you should use 69.3.

the number of years for the economy to double = 72/8 = 9 years, so 9 plus 20 = 29 years. Since the question asks at what age the economy should have more than doubled, it would be a little over 29, and in this case it is 30.

You can always check which number is more exact calculating 1.08⁹ = 1.999

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