CA Foundation · Quantitative Aptitude · Ratio and Proportion, Indices and Logarithms
A ratio a : b is such that (a + b) : (a − b) = 7 : 3. By componendo-dividendo, the value of a : b is:
The ratio a : b is 5 : 2. Applying componendo and dividendo to (a+b)/(a−b) = 7/3 gives a/b = (7+3)/(7−3) = 10/4 = 5/2. Checking with a = 5 and b = 2 gives 7 : 3.
- A5 : 2Correct
- B7 : 3
- C2 : 5
- D4 : 3
Explanation
Using componendo-dividendo, ((a+b)+(a−b))/((a+b)−(a−b)) = (7+3)/(7−3), so 2a/2b = 10/4 = 5/2. Hence a : b = 5 : 2. Check: a=5, b=2 gives 7 : 3. Option 2 wrongly takes the given ratio itself.
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