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Casting Out Nines: A Math Computation Checking Strategy
It's a mathematician's dream come true. An easy trick for checking mathematical computations, without a calculator! Believe it or not, it works with all four operations.
PBS
Pbs Kids: Cyberchase: Counter Example Game Show
Play this interactive game and find the one counter example given by the 9 stars playing the game. It will be the one example that doesn't fit the statement given.