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Problems: finding a part
Textbook Part 3, pp. 20–21
GoalWhen the whole and one part are known, find the other part by subtracting.
New words
whole − part = part · butun − qism = qismaddend · qo‘shiluvchipart (of a machine) · detal
Explanation
Since part + part = whole, whole − part = part. When a problem gives the whole and one part and asks for the other, we subtract. It is the same as finding an unknown addend: _ + 4 = 13 → 13 − 4 = 9.
Worked examples
46 parts were prepared for robotics class and 36 were used for a robot: 46 − 36 = 10 left.
24 curved lines + ? broken lines = 69 lines → 69 − 24 = 45.
Class activity
“Box secret”: a box holds a known number of blocks (the whole is written on it). Some are on the table. Children work out how many are still in the box, then open it to check.
Practice
1
Sum 13, second addend 4. First addend?
9
2
17 triangles + ? squares = 79 shapes
62
3
What must be added to 17 to make 20?
3
4
62 cones + ? cylinders = 89 solids
27