# More comparisons: Comparing heights

Achievement Objectives
NA2-3: Know the basic addition and subtraction facts.
NA2-3: Know the basic addition and subtraction facts.
Specific Learning Outcomes

Recall addition and subtraction facts to 20.

Description of Mathematics

Number Framework Stage 5

Required Resource Materials
Activity

#### Using materials

Problem: Kalila and Holly are measuring the height of the plants they have grown. Kalila’s plant is fourteen cubes high, and Holly’s is eight cubes high. How much taller is Kalila’s plant than Holly’s?

In pairs, one student is Kalila and the other Ngaire.
They build fourteen and eight units high, with interlocking cubes.
Look to see which students make the connection that the problem is solved by working out either 14 – 8 or 8 + ? = 14.
Record whichever of these arises in the discussion on the board or in the modelling book.
Discuss why the answer is six, and record this on the board or in the modelling book.

Examples: Comparison word problems and recording for: 3 + ? = 7, 5 + ? = 10, 9 + ? = 13, 6 + ? = 11, ? + 8 = 12 …

#### Using imaging

Problem: Kelly has a plant eight cubes high, and Tony has a plant three cubes high. How much taller is Kelly’s plant than Tony’s?

Shield parallel lines of eight and three interlocking cubes.
Ask the students to image the extra ones on Kelly’s line and how many there are.
Record 3 + 5 = 8 or 8 – 3 = 5 on the board or in the modelling book, depending on how the students solve the problem.

Examples: Comparison word problems and recording for: 10 + l = 17, 11 + l = 19, 12 + l = 16, 16 + l = 20 …

#### Using number properties

Problem: Tara’s skipping rope is 100 cm long. Lila’s skipping rope is 23 cm shorter than Tara’s. How long is Lila’s skipping rope?

In groups, have the students discuss how to compare the two lengths.
Discuss why the answer is found by 100 – 23.
Record 100 – 23 = 77 on the board or in the modelling book.

Examples: Comparison word problems and recording for: 77 + ? = 81, 38 + ? = 42, 56 + ? = 64, 68 + ? = 77, ? + 87 = 95 …