Written subtraction

Use the H–T–O model on the right. Regroup only when a place does not have enough to take away.

H
T
O
0
4
2
−
0
1
7

H–T–O place-value model

42 − 17 = ?
Next:There are not enough ones. Exchange 1 ten for 10 ones.
Take away17
Taken away so far0
H0
T0
O0

Regrouping changes the form of the number, not its value. Taking away changes the value.

What remains Tap a red take-away group, then tap its matching H, T or O box.
Remaining value: 42. Exchange if a place does not have enough.
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