Answer:
25%
Explanation:
The first doubling, from 20 to 40 occurs in a little more than 3 years, so the multiplier each year is a little less than 2^(1/3) ≈ 1.26. That is, each year is a little less than 26% more than the previous year.
The graph also goes near the point (8, 120), so grows by a factor of 6 in 8 years. That suggests a multiplier of 6^(1/8) ≈ 1.251. Each year is about 25.1% more than the previous year.
Both of these multipliers represent yearly growth rates near 25%.
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Using the "rule of 72", the product of doubling time and percentage growth is about 72. So, for a doubling time of 3 years, the percentage growth is predicted to be near 72/3 = 24 percent.
All of these estimates help you choose the correct answer: 25%.