Interview Q&A / Aptitude

1. If A : B = 2 : 3 and B : C = 4 : 5, what is A : B : C?

   8 : 12 : 15. Make the common term B equal in both ratios. B is 3 in the first and 4 in the second, so scale the first by 4 and the second by 3: A : B = 8 : 12 and B : C = 12 : 15.

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2. Two numbers are in the ratio 3 : 5. If 9 is added to each, the ratio becomes 3 : 4. Find the numbers.

   9 and 15. Let them be 3x and 5x. Then (3x + 9)/(5x + 9) = 3/4, so 12x + 36 = 15x + 27, giving x = 3. The numbers are 9 and 15, and 18 : 24 is indeed 3 : 4.

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3. What are the fourth proportional, third proportional and mean proportional, with an example of each?

   For a : b = c : d, d is the fourth proportional, d = bc/a (4, 9, 12 gives 27). For a : b = b : c, c is the third proportional, c = b^2/a (4, 6 gives 9). The mean proportional between a and b is the square root of ab (9 and 16 give 12).

   BeginnerQuick answer1 min read