Compute with Mass

Teacher: Imagine that the total on the Add Pile is 47. Robbie wants to play a 6 card. What strategy would you use to add 47 and 6?

Linda: I would count on my fingers. I put 47 in my head and then I counted on: 48, 49, 50, 51, 52, 53.

Romesh: I did the same thing but I looked at the number line.

Teacher: So you both counted on. You just used different tools—fingers and the number line. Is there a different way to add it in your head?

Jessie: I went up to 50 first. I took 3 from the 6, because 3 is the partner number for 7. So that makes 50 and then I have 3 left. So that’s 53.

Teacher: Jessie went to the nearest ten first, which was 50, before adding on. He was thinking of the make-ten strategy when he added the 3 to make the next ten. Did anyone do it a different way?

Michael: I know my addition facts. So I thought that it is like adding 7 plus 6, except it is forty-seven plus 6. 7 plus 6 is 13, so 47 plus 6 is 53.

Faith: I thought of 47 as 40 + 7. Then I added 7 + 6 = 13 and 40 + 13 = 53.

Teacher: Now the total on the Add Pile is 53. What card would you place on the pile?

Mark: I would play a 3 card. To add 53 + 3, I would use doubles. 3 + 3 is 6, so 53 + 3 = 56.

Teacher: As you play the game, think of efficient strategies you can use to add a two-digit number and a one-digit number.