Checking Your Answer by Working Backward to Where You Started

Look for this idea outside of your lessons. Careful workers check. A pilot rechecks fuel, a nurse rechecks a dose, and a builder rechecks a measurement before cutting. This is worth learning because finding your own mistakes is a mark of a real mathematician.

Watch for it today, and when you spot it, tell someone what you noticed and how you knew. Ask yourself where else the same idea might be hiding, then go and look.

Let us look at this together. Here is how to check your own work. If you solved 15 minus 6 and got 9, add your answer back: nine plus six is fifteen. You landed where you began, so your answer is right.

If you had gotten eight, the check would give fourteen, and you would know something was off. Checking takes a few seconds and catches most mistakes before anyone else sees them.

Here is a caution. Checking only works if you truly redo the work rather than glancing at it. Actually add your answer back and say the total out loud. Eyes are good at seeing what they expect, so make your check real. Say it out loud once, and then try it with real objects.