How do kids round decimals with a number line?
To round on a number line, kids write the two "neighbor" numbers the number sits between, mark the halfway point, and see which neighbor it is closer to. 3.47 sits between 3.4 and 3.5, past the halfway point of 3.45, so it rounds to 3.5.
How you probably learned it
You learned a rule: look at the digit to the right. If it is 5 or more, round up. If it is 4 or less, round down.
How your kid is learning it
Your kid draws it first, so they can see why the rule works. The rule comes later, as a shortcut for something they already understand.
The three steps
- Find the two neighbors. For "nearest tenth", they are the tenths just below and just above (3.4 and 3.5).
- Find the halfway point (3.45) and put it in the middle.
- Place the number. Whichever neighbor it is closer to is the answer. Exactly halfway rounds up.
Why bother with the picture?
The rule is easy to misapply with decimals. Rounding 1.952 to the nearest tenth, some kids write 1.10 by mistake. On a number line they can see 1.952 lands between 1.9 and 2.0, closer to 2.0.
