Identifying Subtraction Patterns Over Increasing Place Values

Instructor: T.J. Hoogsteen

T.J. is currently a grade 5 teacher and Vice-Principal. He has a master's degree in Educational Administration and is working toward an Ed.D. in Educational Leadership.

In this lesson, identifying subtraction patterns over increasing place values will be covered. The strategy taught will include using basic facts to help find solutions to more advanced problems. There will be a quiz at the end.

Basic Facts and Advanced Problems

''Just like riding a bike'' is an old saying that gets used a lot to show that once people know how to do something, it stays with them forever. In this way, 'riding a bike' is a lot like learning basic math facts. Once a person knows addition, multiplication, subtraction, and division facts, they are not going to forget them.

These basic facts, once known, can also help a person figure out more advanced problems. Those more advanced problems is what this lesson will cover, specifically identifying subtraction patterns over increasing place values.

Subtraction Patterns

So how can subtraction patterns be identified? First, as mentioned, it's important to know the basic facts. Take an equation like 3 - 1 for example. I know that 3 - 1 = 2. But how can knowing that help as place values increase? Well as long as the minuend (the number which is being taken away from) and the subtrahend (the number being subtracted) each increase by the same place value (or each have the same number of zeros) it can be simple. Take 30 - 10 for example. If I know 3 - 1 = 2, then to figure out 30 - 10 I just subtract the numbers in the tens place (3-1=2), and put the same number of zeros the numbers had in the equation into the answer (1 zero). So the answer to 30 - 10 = 20. The same can be done to figure out 300 - 100. Look at the picture below to see the pattern.

3 - 1

You will notice that each time, in each equation, the place value increased. This means a zero was added to each number in the equation. Also the first number in the answer (2) stayed the same, but the number of zeroes in the answer match the number from the starting equation.

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