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Inverse problems
Textbook Part 4, pp. 62–63
GoalWrite and solve the three inverse problems for one situation; complete a diagram.
New words
bowling pin · keglithere were / broke / are left · bor edi / buzildi / qoldidiagram · sxema
Explanation
In a “there were — went — are left” story, any of the numbers can be the unknown. Left unknown: there were − went. Went unknown: there were − left. There were unknown: went + left.
Worked examples
Nozim knocked down 3 of 10 pins: 10 − 3 = 7 left.
3 were knocked down and 7 are left. At first: 3 + 7 = 10 pins.
Class activity
Mini bowling: 10 plastic bottles and a ball. After each throw children ask and answer all three inverse questions.
Practice
1
There are 10 pins and 7 are still standing. How many were knocked down?
3
2
There were 18 toys; 16 are left. How many broke?
2
3
x sports books were borrowed; 5 were returned and 4 are still out. The equation?
x − 5 = 4, x = 9
4
x − 14 = 25. x = ?
39