GRE General TestQuantitative ReasoningMedium
A botanist is tracking the growth of a plant. The plant's height increases by 20% each week. If the plant measures 50 cm today, what will its approximate height be after 3 weeks?
- A72.0 cm
- B90.0 cm
- C86.4 cm
- D60.0 cm
Show answer & explanationAnswer & explanation
Correct answer: C. 86.4 cm
To find the height after 3 weeks, apply a 20% increase for each week sequentially. This involves multiplying the current height by (1 + 0.20) for each week.
Why the other options are wrong
- A. This is the height after 2 weeks (50 * 1.2 * 1.2).
- B. This is incorrect; likely a linear calculation or misapplication of the percentage.
- D. This is the height after only 1 week (50 * 1.2).
Compound Percentage Increase
When a quantity increases by a certain percentage over multiple periods, the increase in each period is applied to the new, larger base from the previous period.
- To increase by P percent, multiply by (1 + P/100).
- For n periods, the final value = Initial Value * (1 + P/100)^n.
- This is a form of exponential growth.
Memory trick: Grow by Factor, Power by Time: Find the growth factor, then raise it to the number of periods.