Answer:
a. the investment earns 4%
b. yes
Step-by-step explanation:
The "rule of 72" says that an investment earning compound interest at x% will double in value after 72/x years. That is, ...
f(x) = 72/x
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<h3>a.</h3>
We interpret f(4) to mean Becky's friend is interested in the doubling time for an investment that earns 4% interest.
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<h3>b.</h3>
Using the above formula, ...
f(4) = 72/4 = 18
The friend's math is correct.
