PrepSwift Quant Tickbox Quiz #14 Question 9

GRE Quant Problem Solving
1

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In this problem, I tried using the formula: total = A + B - Both (which I got 20)
But, after watching solution video, I wanted to know why my formula didnt work, and I am thinking maybe, I should have used Total = A + B - Both + Neither. Am I understanding the solution correctly?

Thank you

2

Yes,
Total = A + B - Both + Neither
100 = 80 + 40 - B + N
100 -120 = - B +N
=> B - N = 20 => B = 20 +N Hence B > or = 20.
The best way however is to analyse this via Venn Diagram to make things clear.