Math basics › When you're stuck

How to check your own work

Substitute back

The strongest check there is. If x = 3 solves the equation, putting 3 in makes both sides equal. This works for almost every 'solve for' problem you will meet.

Ask whether the size is sensible

A length that came out negative, a probability above 1, a discount bigger than the price — something went wrong, and you know it before you check a single line.

Estimate first, then compare

Round everything and do it roughly in your head before the real calculation. If the answer is nowhere near, look again.