Abbie Rules Tidy Numbers

In class today we were  learning how to use tidy numbers to answer problems like 

72-49= ?

We can use place value but it is hard on this problem

 A tidy number is 10s 

You can use you prior knowledge and use your rounding and family of facts to help too.

So you would change 72 into 70

70-49 = 21  and then you to have add the 2 back on from the 72

21 + 2 = 23

So  the answer is 23

We can use family of facts to check: 

49 + 23 = 72

Here is a photo of mrs o and us learning about tidy number and Cooper and Asha working together

 

  By Abbie