D. Solve 3-digit column subtraction with 2-step exchanges with and without using a disk model



Subtract 3-digit numbers that require a 2-step regrouping. A 2-step regrouping is done when there are not enough ones to subtract, and the tens of the minuend is zero. This requires regrouping 1 hundred as 10 tens, and then regrouping 1 ten as 10 ones