CA Foundation · Quantitative Aptitude · Ratio and Proportion, Indices and Logarithms
The third proportional to 8 and 12 is:
The third proportional to 8 and 12 is 18. It is the number x such that 8 : 12 = 12 : x, so x equals 12 squared divided by 8, which is 144 divided by 8, giving 18.
- A16
- B18Correct
- C24
- D20
Explanation
The third proportional x to a and b satisfies a : b = b : x. So 8 : 12 = 12 : x, giving x = 144/8 = 18. The option 16 wrongly continues the difference of 4, and 24 wrongly doubles 12.
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