Krispo is 10%. Bruno is 2%.
Question. Suppose we wanted the final solution to be 6% (not 4%). Because 6 is the midpoint between 10 and 2, wouldn't it then be clear that we would need the final solution to be half of each, and that ratio would be 1:1? It is helpful to visualize this on the number line:
Here we want the final solution to be 4%. So it looks like this:
Because the grand average is skewed towards Bruno, in order to make the final solution 4%, clearly we need more Bruno than Krisp. In fact, because 4 is only 2 units away from 2 but 6 units away from 10, we need 6:2 or 3:1 as much Bruno as Krisp or 1:3 Krisp to Bruno
TAKEAWAY: The amount of skew is inversely proportional to the relative quantities of each item. If we have two groups, A, and B, then we have ("x" and "y" represent distance from the total average):
Average of A-------x-------Total average------y--------Average of B
(# in A)/(# in B) = y/x
This concept recurs fairly frequenly on the GMAT, especially in Data Sufficiency questions. If x and y are integers, then using this approach is quick and effective.
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