Variables & Expressions
Put a number in the box, and the expression's value follows
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The □ in an expression is like a mystery box: the number inside can change, and that number is called a variable. As soon as the box changes, the value of 2×□+3 changes with it. Play with the box to feel how a variable and an expression move together, then practice evaluating the expression when the box is given a fixed value.
A mystery box □ holds a changing number — a variable. Adjust it with +/− and watch 2×□+3 change live; then take the challenge: given □=4, evaluate it.