Modelling subtraction by regrouping a ten
If there are not enough ones to subtract, exchange one ten for ten ones. Show that the total value remains unchanged instead of relying only on “borrowing”.
Try it yourself first.
Solve 42 − 17 with tens and ones drawings. Show 42 first as four tens and two ones, then regroup it.
View the solution or example answer
42 is also three tens and twelve ones. Subtract seven ones and one ten to leave two tens and five ones: 25.
Your next step.
Check with addition: 25 + 17 = 42. If the student cannot explain regrouping, return to the model before adding more calculations.
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