Third Grade - November 3rd - 7th, 2008

This week, third graders are focusing on how to find the difference between a 2-digit number and a number over 100 (128 - 36). Students have already worked on finding how far a number is from 100. Students should be able to reason that 36 is 4 away from 40 and then 60 away from 100 (36 + 4 = 40 and then 40 + 60 = 100). So, 36 is 64 away from 100 (36 + 4 + 60 = 100). Students are now reasoning that if 36 is 64 from 100 and 128 is 28 from 100, then the difference between 36 and 128 is 64 + 28, or 92.