This understanding treats a two-digit number as tens and ones and explains regrouping as decomposing one ten into 10 ones when the minuend has fewer ones than the subtrahend, while preserving the number’s value. It supports finding nonnegative differences of two-digit whole numbers with place-value notation and the standard algorithm, interpreting the result as the amount remaining, and checking by addition; multi-digit subtraction and regrouping across multiple place values are outside this scope.
To subtract two-digit numbers, subtract the ones first and then the tens.
Example:
Look at the ones.
We need to subtract ones from ones, but is too small.
Regroup one ten.
Take ten from the tens. This leaves tens.
Trade that ten for ones:
Subtract the ones.
Subtract the tens.
Put the tens and ones together.
Check your answer by adding:
So, the difference is .
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