Math Brain Teaser #20

From Billy-B's legendary 1001 Puzzle Collection — preserved on Puzz.com since 1998.

Puzzle #20

All of the students at a college are majoring in psychology, business, or both. 73% of the students are psychology majors, & 62% are business majors. If there are 200 students, how many of them are majoring in both psychology & business?

Reveal Answer

If 73% of the students are psychology majors, we know that 27% are not psychology majors — By the same reasoning, 38% are not business majors, because 62% of the students do major in business. So: 27 + 38 = 65 65% of the students are not majoring in both psychology & business, so 35% are double majors, a total of 70 students.

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