[mommaharding]

Well, I'm only a 3rd grade teacher, but it looks to me like they found similar denominators.

For example, 4/9 - 1/5 - 1/4
4/9 is close to 4/10 (2/5)
1/5 (1/5)
1/4 is close to 1/5

So that would explain their estimate.

Same for 2nd.
5 and 24/32 would be 5 and 3/4
3 and 8/16 would be 3 and 1/2

Not sure if that helps, but it makes sense to me.