Two-Digit Number that Certain Sum and Difference (K-1st Graders Only)

The K-1st Grade classes explored two-digit numbers that had a sum of a certain number and a difference of a certain number. This challenge causes them to think about addition and substraction at the same time and strategically look for patterns.

First, I asked the children to give me several two digit numbers. We then looked at the sum of those digits and the difference. This proved to be a very easy exploration for them. For example, the number 51 has a sum of 6 and a difference of 4. When we say difference, we mean positive difference. So the number 15 has the same sum and difference.

Second, I only told them the sum and difference and they had to come up with the number. For example, if a number had a sum of 10 and difference of 2, they would have to first think of which two digits had a sum of 10: 9 and 1, 8 and 2, 7 and 3, 6 and 4, and 5 and 5. Which one of these has a difference of 2? Of course, only 64 and 46 would work.

The attached worksheet and solution pages were given to them to work in teams to solve these patterns.

AttachmentSize
Two-Digit_Number_that_have_Sum_and_Difference_of_......pdf26.27 KB
Two-Digit_Number_that_have_Sum_and_Difference_of_....._solutions.pdf28.92 KB