74
How units of length are related
Textbook: Part 3, lesson 74, pp. 19–21
GoalThe rule linking units of length: big unit to small unit – multiply; small unit to big unit – divide.
New words
multiplying · ko‘paytirishdividing · bo‘lishrule · qoidamixed measure (e.g. 3 m 5 dm) · aralash o‘lchov
Explanation
The chain of length units: 1 km = 1 000 m, 1 m = 10 dm, 1 dm = 10 cm, 1 cm = 10 mm. Going from a big unit to a smaller one, multiply by the number linking them: 4 m = 40 dm. Going from small to big, divide by it: 600 cm = 6 m. To calculate with mixed measures, change them to the smallest unit.
Worked examples
4 m = 40 dm = 400 cm = 4 000 mm; 6 300 cm = 63 m.
3 m 2 dm − 85 cm = 320 cm − 85 cm = 235 cm = 2 m 35 cm.
Class activity
“The chain”: the chain of units is drawn on the board. Each child changes the number on a card to the given unit and writes “×10” or “:10” over the arrow.
Practice
1
7 m = ? mm
7000
2
50 000 dm = ? km
5
3
(2 km 100 m + 1 km 900 m) : 4 = ? m
1000
4
The older brother’s fishing rod is 4 m 20 cm and Sardor’s is 2 m 85 cm. By how many centimetres is the brother’s rod longer?
135
5
From a rope 12 m long, 9 pieces of 7 dm each were cut. How many decimetres of rope are left?
57