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Class 7 Operations with Integers: cheat sheet
CBSE Mathematics. Adding, subtracting, multiplying and dividing negative numbers, and the sign rules that make it work.
Key ideas
- On the number line, numbers increase to the right: −5 is less than −2.
- Subtracting a number is the same as adding its opposite: 4 − (−3) = 4 + 3 = 7.
- Multiplying or dividing two numbers with the same sign gives a positive answer; different signs give a negative answer.
- A product of several numbers is negative when an odd number of them are negative.
- Zero times any integer is 0; division by 0 is not defined.
Remember
| Signs | (+) × (+) = +; (−) × (−) = +; (+) × (−) = − |
| Subtracting a negative | a − (−b) = a + b |
| Example | (−9) × 5 × (−6) = (−45) × (−6) = 270 |
Watch out
- Saying −5 is bigger than −2.
- Forgetting that minus a negative becomes plus.
- Counting the signs wrong when multiplying three or more negatives.
Worked example
Find: (−9) × 5 × (−6)
Working: (−9 × 5) = −45; −45 × (−6) = 270
Answer: 270
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