Problems like this makes my kiddos nuts! I have finally figured out a simpler way to help them subtract
accurately without any "magic" numbers showing up! Maybe you all have already figured this out, but just incase there are others who were struggling with this as I have been, I thought I would share a teaching strategy.
My kids know they need to borrow from the zero, but they cannot figure out how or what number that silly zero turns into. I started asking my kids to look at the next number beside the zero and make it a double digit number. In this case, we would look at 30 instead of just 0. I tell my kids this is the same as 30 tens. Then, I ask my kids, "What number comes just before 30?" It takes some of them a few seconds to think of the answer, but they can count backward and figure out that 29 comes just before 30. So we cross out 30 tens, make it 29 tens, and add the 1 ten in front of the number in the one's place.
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