Unknown component and change of the sum
Find the unknown addend, minuend and subtrahend by rule, compare expressions without calculating and watch how the sum changes.
- Germany: grade 1
- Ukraine: grade 1
- Russia: grade 2
Guide
In Ukrainian Grade 1 books an unknown component in a sum with a box or a question mark is found by a rule. To find an unknown addend, subtract the known addend from the sum. To find an unknown minuend, add the subtrahend to the difference. To find an unknown subtrahend, subtract the difference from the minuend.
In Grade 2 children learn to predict how the result changes when one component changes. If one addend grows by 2 and the other stays, the sum also grows by 2. This lets you compare expressions without calculating: 8 + 5 is less than 8 + 7, because the first addends are the same and 5 is less than 7.
Apples and counters help you see the rule. Then you can use it with any numbers.