134
Order of operations
Textbook: Part 4, lesson 125, pp. 20–21
GoalCalculate longer expressions with and without brackets in the right order; write an expression for a problem.
New words
operation · amalstep · qadamwriting an expression · ifoda tuzishchecking · tekshirish
Explanation
In a longer expression: first inside the brackets, then multiplication and division, then addition and subtraction. (27 : 3 + 15) − 18: inside the brackets first 27 : 3 = 9, then 9 + 15 = 24; then 24 − 18 = 6. Writing an expression: one street has a new houses, another has b, and c are finished. Houses left: a + b − c.
Worked examples
29 + 14 : 2 + 42 = 29 + 7 + 42 = 78.
(46 + 54) : 10 + 56 = 100 : 10 + 56 = 10 + 56 = 66.
Class activity
“Expression workshop”: small groups turn a simple story (for example, 3 boxes with 5 apples each, 4 were eaten) into an expression: 3 × 5 − 4. Another group calculates it.
Practice
1
(27 : 3 + 15) − 18 = ?
6
2
29 + 14 : 2 + 42 = ?
78
3
(46 + 54) : 10 + 56 = ?
66
4
A garden has 14 apple, 20 pear and 6 pomegranate trees. All are planted in 4 equal rows. How many trees are in each row?
10
5
One street has a houses and another has b houses being built, and c are finished. Write an expression for the houses left.
a + b − c