Estimating fractions help
 

Usually i tell my students to use benchmark fractions (1/2, 1/3, 1/4, 1/10) to do estimation problems but i am a little confused at how they arrived at the estimation for the problem given. Please help!!


Problem: 1 - 4/9 - 1/5 - 1/4

Estimation: 1 - 2/5 - 1/5 - 1/5

Another one

Problem: 5 and 23/32 - 3 and 7/16

Estimation: 5 and 3/4 - 3 and 1/2

Possibility
 

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.

Thanks
 

Thanks for your help.