150
The distributive property
Textbook: Part 4, lesson 140, pp. 52–53
GoalProblems with the distributive property; finding a missing number; converting units of length.
New words
missing number · tushirib qoldirilgan sontwo ways · ikki usulunit of measure · o‘lchov birligicorrecting a mistake · xatoni tuzatish
Explanation
Finding a missing number: in (3 + x) × 5 = 35 first find that the sum in brackets is 35 : 5 = 7, then x = 7 − 3 = 4. We solve a problem two ways: each of 4 classes has 5 boys and 5 girls: 4 × (5 + 5) = 4 × 10 = 40 or 4 × 5 + 4 × 5 = 20 + 20 = 40. Converting centimetres: 245 cm = 2 m 45 cm = 2 m 4 dm 5 cm.
Worked examples
(x + 5) × 4 = 32: x + 5 = 8, x = 3.
Wire for 9 poles, 2 m + 4 m each: 9 × (2 + 4) = 54 m.
Class activity
“Hidden number”: the teacher writes (□ + 4) × 3 = 18. Children first find what is in the brackets (18 : 3 = 6), then the hidden number (6 − 4 = 2), and explain aloud.
Practice
1
(3 + x) × 5 = 35, x = ?
4
2
(x + 5) × 4 = 32, x = ?
3
3
From each of 4 classes, 5 boys and 5 girls went to the circus. How many pupils went in all?
40
4
A stadium has 9 lamp posts. Each post needs 2 m and 4 m of wire. How many metres of wire are needed in all?
54
5
Split 245 cm into m, dm and cm.
2 m 4 dm 5 cm