Lesson 4 of 11
A minus that reaches every term
Show on a big screenRice costs ₹30 a kilo. A discount takes ₹2 off each kilo. What do 7 kilos cost?
Step 1 of 4
- 7 × (30 − 2).
- 7 × 30 = 210.
- − 7 × 2 = −14.
- 210 − 14 = 196. Each term keeps its own sign.
A minus that reaches every term
Each kilo now costs 30 − 2 = ₹28. So 7 kilos cost 7 × 28 = ₹196.
Rule: every term inside a bracket is multiplied by the number outside. Each term keeps its own sign when the bracket opens.
- 7 × (30 − 2) = 7 × 30 − 7 × 2 = 210 − 14 = 196
- 6 × (50 − 4) = 6 × 50 − 6 × 4 = 300 − 24 = 276
5(2m − 3)=5 × 2m − 5 × 3=10m − 15, and atm= 4 both give 25
Watch out!
Writing 7 × (30 − 2) as 7 × 30 − 2 gives 208. That mistake takes only ₹2 off the whole bill. The real discount is 7 × 2 = ₹14, so the bill is ₹196. With one kilo the mistake happens to match. With seven it does not.
Pick a reading. Slide the kilos. Match the real bill.
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Try the lab to finish this lesson.