Lesson Plan
“Subtract One” Strategy: Subtracting From Zeros Without Borrowing
Many students cringe when they see a subtraction problem with multiple zeros. The “Subtract One” strategy in this lesson involves reducing the top number by one to turn the 0 digits into 9’s and then adding the one back in at the end.
Grade:
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Learning Objectives
Students will be able to use the Subtract One strategy to subtract from numbers with multiple zeros (i.e. 4,000 - 347).
Introduction
(5 minutes)- Write the problem 5,000 - 2,384 on the board. Ask for a student to come to the board and make a tally mark for each step you perform to solve the problem. Use the traditional borrowing method and count the steps. It’s not important that these are exact.
- Observe how many steps it took to borrow, just to be able to perform the subtraction in each column.
- Tell students that with each step involved, the chances of an error increases, and it takes more time.
- Explain that they are going to learn a more efficient strategy for subtracting from numbers with multiple zeros in the “top number,” called the Subtract One strategy.