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Equality 2

Directions: Use the digits 1 to 9, at most one time each, to fill in the boxes to create a true number sentence with the greatest possible value.

Hint

Hint

What does the equal sign tell you?
How do we know if both sides of the equal sign have the same value?
What is the greatest possible value each side of the equal sign can have?

Answer

Answer

The greatest value that the side with the subtraction sign can have is 8 (from 9 – 1). So, possible answers include:

2 + 6 = 9 – 1
6 + 2 = 9 – 1
3 + 5 = 9 – 1
5 + 3 = 9 – 1

4 + 4 = 9 – 1 is not an answer because the 4 is used twice.

There might also be conversations about whether 2 + 6 = 1 – 9 is an answer. This may lead into conversations about how addition is commutative (1 + 4 equals 4 + 1) but subtraction is not (1 – 4 does not equal 4 – 1).

What students MIGHT think is correct, but is NOT correct is something like:

4 + 5 = 9 – (any number other than 0)

This would be because 4 + 5 = 9. However, both sides of the equal sign must have the same value, and they do not when you subtract another number other than zero.

Source: Robert Kaplinsky

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