20
Problem solving (practice)
Textbook: Part 1, lesson 20, pp. 61–63
GoalPractise multi-step problems by writing an expression.
New words
multi-step problem · ko‘p amalli masalachange (money back) · qaytimequation · tenglamasum · yig‘indi
Explanation
We split a multi-step problem into parts and decide what can be found at each step. Then we write the whole solution as one expression, keeping the order of operations: brackets first, then multiplication and division, then addition and subtraction. In an equation we find the unknown part by the rule.
Worked examples
Five notebooks at 2 400 sum each cost 2 400 × 5 = 12 000; paying 20 000 sum gives 20 000 − 12 000 = 8 000 sum change.
(x + 5) × 3 = 36 → x + 5 = 36 : 3 = 12 → x = 12 − 5 = 7.
Class activity
“Find the expression”: the teacher reads a problem; children write it as a single expression and compare on the board.
Practice
1
Dilnoza bought 3 kg of apples at 12 000 sum and 2 kg of pears at 15 000 sum and gave 100 000 sum. How many sum change did she get?
34000
2
A cyclist rode 3 hours at 14 km/h, then 2 hours at 18 km/h. How many km did she ride in all?
78
3
6 craftsmen each make 8 chairs a day. In how many days do they make 240 chairs?
5
4
Solve (x + 15) × 4 = 100.
10