lesson
Find the unknown part
1 · Learn
A missing number can be a part, a whole or an amount removed. Think about what the number represents before choosing an operation.
If 164 + __ = 250, the missing part is the difference between 250 and 164. Subtract to find it, then put it back into the original statement.
2 · Worked example
For __ − 75 = 130, the starting whole must be 130 + 75 = 205.
3 · Your turn
Solve 425 − __ = 280. Check your answer.
Check your answer
145. The check is 280 + 145 = 425, so 425 − 145 = 280.
4 · Apply your learning
Make a short word problem for a missing-part calculation and explain what each number means.
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Use objects or a drawn model before relying on a rule. Explain each step, check the units and revisit with varied examples. An adult can read the instructions without supplying the answer.
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