# The missing ones and tens

Achievement Objectives
NA1-1: Use a range of counting, grouping, and equal-sharing strategies with whole numbers and fractions.
Specific Learning Outcomes

Solve addition and subtraction problems using groups of ten.

Description of Mathematics

Number Framework Stage 4

Required Resource Materials
Ones and Tens material. E.g. sticks in bundles, BeaNZ, money
Activity

#### Using Materials

Problem:  Marlene is planning a big party for 34 friends. Everyone needs a can of drink at the party but she has only got 21 cans in her cupboard.  How many cans of drink will she have to buy at the shop?

Write on the board and discuss why this amounts to solving 21 +  ? = 34

The students use one and tens materials to solve the problem and their solutions are discussed.

Examples. Word stories and recording for: 15 + ? = 36,  21 + ? = 36,  20 + ? = 46,  31 + ? = 37,  42 + ? = 52,  34 + ? = 46....

#### Using Imaging

Examples. Word stories and recording for: 25 + ? = 46,   31 + ? = 41,  30 + ? = 41, 11 + ? = 18,  42 + ? = 52,  4 + ? = 36....

#### Using Number Properties

Examples. 25 +  ? = 86,  31 + ? = 91,  20 +  ? = 85....

Challenging examples. The students will need to understand the meaning of three digit numbers to do these: 241 + ? = 248,  320 + ? = 345,  643 + ? = 647,  99 + ?  = 109....