CA Foundation · Quantitative Aptitude · Ratio and Proportion, Indices and Logarithms
The mean proportional between 4 and 25 is:
The mean proportional between two numbers is the square root of their product. Here the product of 4 and 25 is 100, and its square root is 10. So the mean proportional is 10, because 4:10 equals 10:25, both reducing to 2:5.
- A10Correct
- B12.5
- C14.5
- D100
Explanation
If x is the mean proportional between a and b, then x² = ab. Here x² = 4 × 25 = 100, so x = 10. The value 12.5 is a common wrong answer that comes from taking the simple average of 4 and 25 (14.5) or half of 25, while 100 is the product, which is not square-rooted.
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