63
Metre, decimetre, centimetre
Textbook: Part 2, lesson 60, pp. 42–43
GoalAdd and subtract lengths in m, dm, cm (with regrouping).
New words
long · uzunshort · qisqaregrouping · o‘tkazishdifference · farq
Explanation
5 m 4 dm 2 cm = 54 dm 2 cm = 5 m 42 cm = 542 cm – the same length written in different ways. When adding remember 10 cm = 1 dm and 10 dm = 1 m: 8 cm + 2 cm = 10 cm – 1 dm moves over. When subtracting and there is not enough, change 1 m into 10 dm and 1 dm into 10 cm.
Worked examples
5 m 4 dm 8 cm + 3 m 7 dm 2 cm: 8 + 2 = 10 cm → 1 dm; 4 + 7 + 1 = 12 dm → 1 m; 5 + 3 + 1 = 9 m. The answer is 9 m 2 dm 0 cm.
8 m 5 dm = 85 dm and 23 m = 230 dm: the difference is 230 − 85 = 145 dm = 14 m 5 dm.
Class activity
“Dinosaur length”: stretch a tape 8 m 5 dm (or 12 m 8 dm) across the room; children check it with steps or a metre rule and compare with their own measurements.
Practice
1
7 m 5 dm 3 cm = ? cm
753
2
5 m 4 dm 8 cm + 3 m 7 dm 2 cm = ? cm
920
3
6 m 4 dm 8 cm − 2 m 5 dm 1 cm = ? cm
397
4
An allosaurus is 8 m 5 dm long and a brachiosaurus 23 m. How many decimetres longer is the brachiosaurus?
145