7. Ratio, Proportion and Variation

Ratio Proportion Variation is a fundamental topic in GMAT Math. Many word problems in the problem solving section of GMAT Math section are essentially ratio proportion questions. 4GMAT's GMAT Math Review Book in problem solving covers the following concepts in this chapter:

1. The meaning of the term ratio and an illustrative example to explain the same
2. The rules governing ratios and fractions
3. Definition and explanation of the term proportion, continued proportion, direct variation and inverse variation
4. 35 solved examples with explanation that helps the process of understanding and also the essential short cuts that would save time in arriving at the solution as and when applicable
5. 21 exercise problems with the answer key and explanatory answers
6. An objective type speed test with around 50 questions with explanatory answers and answer key provided for the speed test

Here is an example of a typical solved example in this chapter.
Sample Question
Question
What is the value of 'x' if it is the mean proportional of x - 4 and x + 8?

Explanatory Answer
As x is the mean proportional of x - 4 and x + 8, we have x - 4 : x :: x : x + 8

Therefore,

Or x2 = (x-4)(x+8) => x2 = x2 + 4x - 32

Therefore, x = 8