A counselor is placing 72 students into at least one of the following classes: Physics, Calculus or Computer Programming. 36 take physics, 36 take calculus and 20 take programming. 7 take calculus and programming, 5 take physics and programming, and 12 take calculus and physics. If 21 take only physics, how many are in all three classes.

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A counselor is placing 72 students into at least one of the following classes: Physics, Calculus or Computer Programming. 36 take physics, 36 take calculus and 20 take programming. 7 take calculus and programming, 5 take physics and programming, and 12 take calculus and physics. If 21 take only physics, how many are in all three classes.

answer is 8

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