M2.2.2 For the adult
Taking away in your head
What is 302 − 298? Do I have to write it down?
What this chapter teaches
The difference is how far apart two numbers are. Count up from the smaller number to the bigger one, using a near ten or hundred as a stepping stone. Taking the smaller digit from the bigger one in each column goes wrong: 302 − 298 is 4, not 196.
Three questions to ask
There is no one right wording. Listen for the idea.
- How far is it from 298 up to 302, and how did you find it?
- Why do we count up from the smaller number to find a difference?
- How can you tell, without working it out, that 196 is too big for 302 − 298?
After the chapter, the learner can
- Take away by counting up from the smaller number
- Find the difference between 302 and 298 without writing
What they copy into their notebook
The difference is how far apart two numbers are. Count up from the smaller number. 298 to 300 is 2. 300 to 302 is 2. The difference is 4.