Solve addition and subtraction problems using groups of ten.
Solve addition and subtraction problems by using place value partitioning.
Number Framework Stage 4 and 5.
Ones and tens material. For example, sticks in bundles, play money etc
Required Knowledge
Before attempting this activity check that the students can:
• Instantly recall the addition facts with answers up to 10.
• Interchange instantly the “ty” words with “tens” e.g. sixty means six tens, fifty means five tens.
The activities that follow are important because they simultaneously help develop addition, subtraction and place value concepts.
Using Materials
Problem: Hemi has 39 sweets and he buys a packet of 20 sweets. How many does he have altogether?
Record 39 + 20 on the board. Get students to model 39 then 20 on tens and ones material. The students work out the answer using material and then discuss the answer. Write 39 + 20 = 59 on the board.
Examples. Word stories and recording for: 35 + 20, 42 + 10, 20 + 34, 30 + 34, 21 + 50, 40 + 27....
Using Imaging
Shielding
Write 34 + 20 on the board and ask the students how they would build 34 and 20 separately. Then hide 34 and 20 under an ice cream container. Ask the students how any tens there are under the container. Discuss the idea that because 3 + 2 = 5 then 3 tens + 2 tens = 5 tens so 34 + 20 must be 54. (It is here that the instant recall of basic facts is needed.) Record 34 + 20 = 54 on the board.
Shielding and Imaging Only:
Examples. Word stories and recording for: 18 + 20, 30 + 24, 23 + 40, 13 + 50, 10 + 46....
Using Number Properties
Examples. 87 + 10, 78 + 20, 20 + 62, 46 + 50, 80 + 17....
Challenging examples. The students will need to understand the meaning of three digit numbers to do these: 340 + 20, 640 + 30, 423 + 20, 50 + 204..