Subtracting a negative number
Rewrite every subtraction as an addition, see subtracting a negative on the line, and work two-digit sums in tens and ones.
- Germany: grade 5
- Iran: grade 7
- Ukraine: grade 6
Guide
This studio follows the Iranian Grade 7 lessons on adding and subtracting integers. The book always rewrites a subtraction as an addition first: 3 − 7 = 3 + (−7).
A negative number such as −5 is the opposite of 5. The opposite of −5 is 5, so −(−5) = 5.
Subtracting a negative number means adding its opposite: −4 − (−5) = −4 + 5 = 1. On the line, instead of hopping left we hop 5 to the right.
You can work two-digit numbers in tens and ones: 34 − 27 = (30 − 20) + (4 − 7) = 10 + (−3) = 7.