Checking Equations

You rarely need the exact answer to know an equation is wrong. Three checks catch most mistakes.

Estimate first: 18 × 7 is about 20 × 7 = 140, so an answer of 96 must be wrong.

Check the last digit: 12 × 6 must end in 2, because 2 × 6 = 12.

Check even and odd: an even number times any number is even, so 14 × 3 = 43 cannot be right.

Practise below — use ← for true and → for false, or the buttons.