2010 AMC 10B Problems/Problem 12

The minimum possible value occurs when 20% of the students who originally answered "No." answer "Yes." In this case, x=20

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The maximum possible value occurs when 30% of the students who originally answered "Yes." answer "No." and the 50% of the students who originally answered "No." answer "Yes." In this case, x=50+30=80

Subtract 20 from 80 to obtain an answer of $\boxed\{\mathrm {(D)} 60}$ (Error compiling LaTeX. Unknown error_msg)