Lesson 8 of 16
Writing your own expression
Show on a big screenYou buy 2 samosas at ₹15 each. You buy 3 pens at ₹25 each. What is the bill?
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Step 1 of 5
- The order: 2 samosas, 3 pens.
- Samosas: 2 × 15 = 30.
- Pens: 3 × 25 = 75.
- Add the terms: 30 + 75 = 105.
- Two friends order the same: 2 × 105 = 210.
The rule
The bill is ₹105.
Write one term for each item: how many × the price. Join the terms with +.
2 × 15 + 3 × 25
Here 2 × 15 is the samosas and 3 × 25 is the pens. Then 30 + 75 = 105.
Two friends order the same. Put the whole bill in brackets. Then the 2 multiplies both the samosas and the pens.
2 × (2 × 15 + 3 × 25)
Check the size with easy numbers. Two samosas near ₹15 each is near ₹30. Three pens near ₹25 each is near ₹75. So a bill near ₹100 is sensible.
| The order | The line | Comes to |
|---|---|---|
| 2 samosas, 3 pens | 2 × 15 + 3 × 25 | 105 |
| 4 cups of tea at ₹12 | 4 × 12 | 48 |
| A ₹40 notebook, ₹10 off | 40 − 10 | 30 |
Watch out!
Two friends need brackets round the whole bill. 2 × 2 × 15 + 3 × 25 doubles only the samosas. It gives 135, not 210.
Try the lab to finish this lesson.