Counting How Many Are in Each Category

This idea walks around your house all day. Inventory counts work exactly this way, and the total check is what catches missing items. This is worth learning because a total check catches errors that a single count would hide. 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.

This is a good thing for a young mathematician to know. After sorting, count each group and write the number beside its label. Red buttons: seven. Blue buttons: four. Green buttons: five.

Now you know more than you did when the pile was mixed. You can also add all the groups to check against the total you started with. If the numbers do not match, something was miscounted or misfiled, and it is worth finding out which.

Here is the check that catches errors. Add all your group counts together and compare with the total pile. If the numbers disagree, you either miscounted a group or put something in the wrong place. Do it carefully rather than quickly, and thank God for a mind that can learn.