GRE General TestQuantitative ReasoningMedium
A data analyst is examining a dataset of monthly website visitors. The number of visitors increased by 20% in January, then decreased by 10% in February, and finally increased by 5% in March. If there were 10,000 visitors at the end of December, how many visitors were there at the end of March?
- A11,500
- B11,800
- C11,550
- D11,340
Show answer & explanationAnswer & explanation
Correct answer: D. 11,340
Apply each percentage change sequentially. January: 10,000 * 1.20 = 12,000. February: 12,000 * 0.90 = 10,800. March: 10,800 * 1.05 = 11,340.
Why the other options are wrong
- A. This incorrectly adds the percentages (20-10+5 = 15%) to the original amount.
- B. This is incorrect; it does not reflect the sequential changes accurately.
- C. This is a plausible distractor, perhaps from a slight miscalculation.
Successive Percentage Changes
To calculate the final value after successive percentage changes, apply each change sequentially to the *current* value, not the original value.
- An increase of X% means multiplying by (1 + X/100).
- A decrease of X% means multiplying by (1 - X/100).
- The order of changes matters unless all changes are increases or all are decreases.
Memory trick: Each step changes the base, not just the start.