132
Order of operations
Textbook: Part 4, lesson 123, pp. 16–17
GoalKnow that multiplication and division are done before addition and subtraction.
New words
is done first · birinchi bajariladithen · keyinmultiplication · ko‘paytirishdivision · bo‘lish
Explanation
If there are no brackets, we do multiplication and division first (left to right), then addition and subtraction (left to right). 20 + 6 × 3: first 6 × 3 = 18, then 20 + 18 = 38. 63 : 7 + 19: first 63 : 7 = 9, then 9 + 19 = 28. It helps to write 1, 2, 3 above the operations.
Worked examples
50 − 24 : 4: first 24 : 4 = 6, then 50 − 6 = 44.
21 + 24 : 6 − 17 = 21 + 4 − 17 = 25 − 17 = 8.
Class activity
“Operation program”: write 28 + 14 : 2 − 5 on the board. Children number the steps (1st division, 2nd addition, 3rd subtraction) and find the result.
Practice
1
30 + 4 × 5 = ?
50
2
63 : 7 + 19 = ?
28
3
18 − 18 : 6 = ?
15
4
21 + 24 : 6 − 17 = ?
8
5
A library had 12 books. 5 books were added to each of 3 shelves. How many books are there now?
27