CA Foundation · Quantitative Aptitude · Ratio and Proportion, Indices and Logarithms
If a, b, c are in continued proportion and a = 4, c = 25, then the sum of b and the third proportional to a and b (taking the positive value of b) is:
The sum is 35. Since a, b, c are in continued proportion, b squared equals 4 times 25, which is 100, so b is 10. The third proportional to 4 and 10 is 100 divided by 4, which is 25. Adding gives 10 + 25 = 35.
- A10
- B35Correct
- C30
- D20
Explanation
Continued proportion gives b² = ac = 100, so b = 10. Third proportional to 4 and 10 is 10²/4 = 25, which is c. The sum is 10 + 25 = 35. The option 30 is wrong because it uses 20 for the third proportional via doubling 10.
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