69
Problem solving
Textbook: Part 2, lesson 69, pp. 93–94
GoalProblem solving: order of operations and mixed problems.
New words
order of operations · amallar tartibiwaste paper · makulaturaremaining · qolganpart (piece) · detal
Explanation
In expressions we do brackets first, then multiplication and division, then addition and subtraction: 640 − 72 : 8 = 640 − 9 = 631. In a mixed problem we do the needed steps one after another. For example, a class planned to collect 60 kg of waste paper; 6 pupils brought 4 kg each and 4 pupils 7 kg each: 6 × 4 + 4 × 7 = 52 kg, so 60 − 52 = 8 kg more are needed.
Worked examples
640 − 72 : 8 = 640 − 9 = 631.
6 × 4 + 4 × 7 = 24 + 28 = 52; 60 − 52 = 8 kg.
Class activity
“Workshop”: groups invent a three-step problem and give it to another group to solve.
Practice
1
Find the value of 640 − 72 : 8.
631
2
A class planned to collect 60 kg of waste paper. 6 pupils brought 4 kg each and 4 pupils 7 kg each. How many kg more are needed?
8
3
A carpenter cut two boards for a bookcase, 25 cm × 80 cm and 30 cm × 80 cm. What is the total area of the boards in cm²?
4400
4
The small tank holds 12 five-litre cans of milk. The large tank holds 4 times as much. How many litres of milk are there in both?
300