Here is a problem I gave to two fifth graders to work a few days ago. You see nine boxes of candy here. Each box contains 52 pieces of candy.
The question says: About how many pieces in all?
The first fifth grader l'll call Sammy. This is how Sammy worked this problem. He said: "Nine is just about ten and 52 is about 50. Ten times 50 is 500. So there are about 500 pieces of candy. (Point to 9 and 52 and write 10 x50 500 while reading this.)
Do you think it was OK for Sammy to use these numbers (point to 10 and 50) instead of these numbers (point to 9 and 52)?
Is this (point to 500) an OK answer to this question (point to About )?
why not? (or) some fifth graders think is not OK. Could you explain to them why you think it is OK?
Now let me show you how Vanessa did the problem. She wrote (write out 9 in standard algorithmic form) and said: "So 500 pieces. Which way do you think is a better way of doing this problem, Sammy's way for Vanessa's way? Why did you choose that way?