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Math Puzzles

Viral math problems, famous puzzles and surprising facts, each answered in the first lines and then explained step by step. Many of them come from questions asked under our videos.

Puzzles
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Puzzles and viral math

Math Puzzles: the essentials

Order of operations

Parentheses first, then exponents, then multiplication and division together from left to right, then addition and subtraction together from left to right. Most viral equations are built on skipping one of these steps.

Why 0! = 1

The factorial n!n! counts the ways to arrange nn different objects in a row. There is exactly one way to arrange nothing (the empty arrangement), so 0!=10!=1. It also keeps the rule n!=n×(n−1)!n!=n\times(n-1)! working at n=1n=1: 1!=1×0!1!=1\times 0! needs 0!=10!=1.