I was wondering, if there is actual mathematical (and "fool-proof") formula which I can apply for evaluating actual value in question that involves subgroups in a set. For example, if I see a question such as "1/3 of a total is female students and 2/3 of the total is female and 1/5 of the total is not a student. How many are neither student nor female?" (not a real question, so might not be a good description), is there any formula that I could apply (eg. sub group ratio x multiplied by subgroup ratio m equals to non-subgroup ratio l)
Some people use this formula: Total = (total of A) + (total of B) - (both A & B) + (neither A nor B)
It's valid, but in my opinion you will have more flexibility with the Double Set Matrix. The GMAT could give you values for any
box in the matrix (for example, "there are 10 things that are A but not B," which isn't directly a term in the formula above). Even worse, the GMAT could give you a relationship between two boxes in the matrix, which again might not fit nicely into a predetermined formula. And, of course, the question could ask for any box in the matrix, not just a simple total or subtotal.
Emily Sledge | Manhattan GMAT Instructor | St. Louis
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