35
Subtracting a number from a sum
Textbook: Part 1, lesson 34, pp. 72–73
GoalLearn subtracting a number from a sum: (a + b) − c.
New words
subtracting from a sum · yig‘indidan ayirishaddend · qo‘shiluvchidrone · dronreserve · zaxira
Explanation
To subtract a number from a sum we can subtract it from either addend and then add the other: (a + b) − c = (a − c) + b = a + (b − c). The number we subtract must not be bigger than the addend we take it from.
Worked examples
(20 + 37) − 7 = 20 + (37 − 7) = 20 + 30 = 50.
(12 + 24) − 14 = 12 + (24 − 14) = 12 + 10 = 22.
Class activity
“Drone show”: two colours of drones are shown on the board (for example 38 and 30). Children find two ways to take away the drones put in reserve.
Practice
1
(20 + 37) − 7 = ?
50
2
(35 + 47) − 5 = ?
77
3
(25 + 24) − 14 = ?
35
4
There were 38 red and 30 white drones. 8 were kept in reserve. How many drones flew?
60