NumihanaThe size of the answer is not limited to the number of digits in each starting number. Adding two numbers close to a thousand can pass one thousand. The operand limit is still three digits; a fourth answer column records the sum accurately.
Work through the example
- Set out 786 + 579. Estimate 800 + 600 = 1,400, so expect a sum over a thousand.
- Ones: 6 + 9 = 15. Write 5 and carry 1 ten.
- Tens: 8 + 7 + 1 = 16. Write 6 and carry 1 hundred.
- Hundreds: 7 + 5 + 1 = 13 hundreds. Write 3 hundreds and carry 1 thousand into a new column. The answer is 1,365. Check 1,365 − 579 = 786.
Why it works
Thirteen hundreds can be regrouped as one thousand and three hundreds. The extra column is part of the answer, even though both operands leave it blank. Read the whole answer aloud to connect the notation to the amount.
A common slip
Stopping after three answer digits would record 365 and lose a thousand. Compare that result with the estimate: adding 786 and 579 must make a number larger than either operand.
For teachers & parents
Use this as an extension within addition of two operands up to three digits. It does not claim that Year 3 requires four-digit operands. In practice, a leading answer cell may be left blank when no thousands digit is needed; a genuine thousands digit must be entered.
Talk it through
Can two three-digit positive numbers make a five-digit sum? Think about the largest possible operands before calculating.
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