Adding and Subtracting Inside the Teens Using Ten as an Anchor

Here is where this shows up in real life. Anchors hold things steady in a current. Ten anchors a teen number so only the small part moves. This is worth learning because holding the ten still keeps big numbers from feeling heavy.

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.

Get your eyes and your fingers ready. Ten makes teen arithmetic simple. For 15 minus 3, leave the ten alone and work with the ones: five take away three is two, so the answer is twelve. For 12 plus 4, add the ones: two plus four is six, giving sixteen.

As long as the ones do not cross ten, the ten sits still and only the ones change. That anchoring makes these problems much lighter work.

Watch out for problems that cross ten, like 15 minus 7. The ten does not sit still there, because you must break it apart. For now, notice when a problem crosses ten and know that it needs a different tool. You will use this idea again and again, so build it strong today.