65
Decimetre, centimetre, millimetre
Textbook: Part 2, lesson 62, pp. 46–47
GoalWrite, add and subtract lengths in dm, cm and mm.
New words
map · xaritadistance · masofaline segment · kesmafar · uzoq
Explanation
Before adding or subtracting, change lengths into one unit – often millimetres. 35 cm 6 mm = 356 mm and 4 dm 28 mm = 428 mm. Then split the result into bigger units again: 743 mm = 7 dm 4 cm 3 mm. Remember 10 mm = 1 cm and 10 cm = 1 dm.
Worked examples
5 dm 6 cm 4 mm + 1 dm 7 cm 9 mm = 564 + 179 = 743 mm = 7 dm 4 cm 3 mm.
7 dm 2 cm 1 mm − 2 dm 5 cm 4 mm = 721 − 254 = 467 mm = 4 dm 6 cm 7 mm.
Class activity
“Map distance”: with a ruler measure Tashkent–Samarkand and Tashkent–Fergana on a map of Uzbekistan. Which is farther and by how many mm?
Practice
1
35 cm 6 mm + 4 dm 28 mm = ? mm
784
2
7 dm 43 mm − 21 cm 7 mm = ? mm
526
3
Lola knows 22 capital cities and Malika knows 31. How many more does Malika know?
9
4
Segment AB is 6 cm 5 mm and its part AC is 4 cm. How many mm is part CB?
25