Review: Adding and Subtracting with Tens

Here is where this shows up in real life. Money, measurement, and inventory all run on tens. This is arithmetic people use at work. This is worth learning because knowing when regrouping is needed prevents most two digit mistakes. 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.

Here is something worth knowing today. You can now add and subtract in tens. Whole tens added or removed change only the tens digit. Ones added past ten bundle into a new ten. Ten more and ten less come instantly, without counting.

Try these: 40 plus 30, 85 minus 10, 27 plus 6. The first two need no regrouping. The third does, because seven and six make thirteen ones, so one new ten gets bundled.

Try sorting problems before solving them. Which of these need regrouping and which do not? Sorting first turns a page of problems into two much simpler piles, and it trains you to notice the structure. Practice this a few times and it will start to feel easy.