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Subtraction Procedure
A Closer Look at the Video
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After watching the Subtraction Procedure video, make sense of the mathematics by taking a
closer look at the problem situation and solution. Use the comments and questions in bold
to help you solve the problems and learn more about subtracting big numbers.
Problem: Zander and K.T. are volunteering at a greenhouse and they noticed a mistake in
the delivery log. Yesterday the greenhouse started with 523 plants and sent out 189 plants.
The logbook says that 523 plants โ 189 plants = 466 plants, but Zander and K.T. know this
is incorrect! What should the logbook say about how many plants are left?
How did KT use estimation strategies to find the error in the logbook? K.T. knew that
523 โ 100 = 423. That is less than 466, the answer in the logbook, and K.T. still needs to
subtract another 89 plants.
What subtraction mistake did Zander discover when looking in the logbook? Zander
looked at each place value and noticed that someone subtracted the smaller number in each
place from the larger number. This is incorrect.
Logbook error: Incorrect thinking:
523 ones place 9 โ 3 = 6
- 189 tens place 8 โ 2 = 6
466 hundreds place 5 โ 1 = 4
Using a model to solve a subtraction problem helps make sense of the procedure. This
video uses flats of 100 plants, rows of 10 plants, and individual plants.
How can you represent 523 with flats, rows, and individual plants?
You can represent 523 by looking at the number of hundreds, the number of tens, and the
number of ones in 523.
The hundreds place is represented by 5 flats, each
containing 100 plants.
The tens place is represented by 2 rows, each
containing ten plants.
The ones place is represented by three individual
plants.
