Practice GMAT Problem Solving Question

The ratio between x and y is 7/9; x and y are increased by 4, what is the ratio between the new values of x and y?

Correct Answer: E

Translate the given information into algebraic equations that can be easily manipulated.
Originally: (x/y) = (7/9)
Note: This DOES NOT mean x and y are 7 and 9 respectively. It only means that "the ratio between x and y is 7/9". Consequently, possible values for x and y are 7 and 9, 14 and 18, 21 and 27, etc.
Set up an algebraic equation for the new x and y.
((x + 4) / (y + 4)) = ?
In order to see if a pattern emerges, try plugging in numbers and using a chart:

x y x + 4 y + 4 (x/y) = (7/9) (x + 4)/(y + 4) = ?

7 9 11 13 7/9 = .777 11/13 = .84

14 18 18 22 14/18 = .777 18/22 = .81

21 27 25 31 21/27 = .777 25/31 = .806
As the above chart indicates, there is no consistent ratio between x and y, and x+4 and y+4. Consequently, the answer choice E is correct.