131
Order of operations
Textbook: Part 4, lesson 122, pp. 14–15
GoalCalculate expressions with only addition and subtraction, or only multiplication and division, from left to right.
New words
order of operations · amallarning tartibileft to right · chapdan o‘nggaone after another · ketma-ketvalue of an expression · ifodaning qiymati
Explanation
If an expression has only addition and subtraction, or only multiplication and division, we work from left to right, one step after another. 126 − 24 + 12: first 126 − 24 = 102, then 102 + 12 = 114. 48 : 6 × 2: first 48 : 6 = 8, then 8 × 2 = 16. If we break the order, the answer changes!
Worked examples
824 − 30 − 12 = 794 − 12 = 782.
15 : 5 × 2 = 3 × 2 = 6 (not 15 : 10).
Class activity
“In order”: each pair copies an expression from a card and writes the result after each step on a new line. Pairs swap and check each other’s work.
Practice
1
126 − 24 + 12 = ?
114
2
824 − 30 − 12 = ?
782
3
15 : 5 × 2 = ?
6
4
48 : 6 : 2 = ?
4
5
A bus had 35 passengers. At a stop 12 got off and 9 got on. How many passengers are on the bus now?
32