Know that addition and subtraction, multiplication and division, and powers and roots, are inverse operations and use this to simplify and check calculations, for example, in reversing arithmetic in “I’m thinking of a number” or “missing digit” problems.

e.g.

\(223 - 98 = 223 + 2 - 100 = 125\)

\(25 × 12 = 50 × 6 = 100 × 3 = 300\)

[see also Calculation and estimation of powers and roots, 3.01b]