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CA Foundation · Quantitative Aptitude · Ratio and Proportion, Indices and Logarithms

If A : B = 3 : 5 and B : C = 2 : 7, then the ratio A : B : C is:

When combining two ratios with a common term, equalize that term. Here B is 5 parts in the first ratio and 2 parts in the second, so multiply the first ratio by 2 and the second by 5, giving A : B : C = 6 : 10 : 35.

  1. A3 : 5 : 7
  2. B6 : 10 : 35Correct
  3. C3 : 10 : 35
  4. D2 : 5 : 14

Explanation

To combine ratios, make the common term equal. A : B = 3 : 5 means A = 3k and B = 5k. B : C = 2 : 7 means B = 2m and C = 7m. Since B is common, 5k = 2m, so multiply the first ratio by 2 and the second by 5 to get A : B = 6 : 10 and B : C = 10 : 35. Therefore A : B : C = 6 : 10 : 35.

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