CA Foundation · Quantitative Aptitude · Sequence and Series
The arithmetic mean of two positive numbers is 25 and their harmonic mean is 16. What is their geometric mean?
The geometric mean is 20. For any two positive numbers, the square of the GM equals the product of the AM and the HM. Here that product is 25 × 16 = 400, whose square root is 20.
- A20Correct
- B9
- C18
- D21
Explanation
For two positive numbers, GM² = AM × HM = 25 × 16 = 400, so GM = 20. Taking the simple average of AM and HM, (25+16)/2 = 20.5, is not valid; 21 is a rounding of that wrong approach.
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