Solve addition and subtraction problems by compensating with tidy numbers.
Number Framework Stage 5
Number Lines (Material Master 5-12)
This problem can be solved by jumping up to 30 then jumping to 71. However,because 23 is some distance from 30, another method, namely adding 50 to the 23 first, is worth learning.
Using Materials
Problem: 23 plus what is 71?
Write 23 + ? = 71 on the board. On the class number line jump 50 from 23 to reach 73. Discuss why we need to jump back 2 and so why is the answer 48. Record 23 + 48 = 71.
Examples. Record and do these problems on first side of the sheet. 24 + ? = 82, 52 + ? = 90, 25 + ? = 91, 13 + ? = 71, 12 + ? = 91, 54 + ? = 72, 45 + ? = 83, 14 + ? = 83 …
Imaging
Use imaging for those students who are struggling.
Using Number Properties
Examples. Record and do these problems on paper: 24 + ? = 82, 52 + ? = 90, 24 + ? = 91, 12 + ? = 61, 82 + ? = 101