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3 pens cost 12 yuan: how much for 5 pens?
At a stationery shop, 3 identical pens cost 12 yuan in total. At the same unit price, how much do 5 such pens cost?
Answer
20
Step-by-step
- 12 ÷ 3 = 4Find the unit price first (reduce to one)
- 4 × 5 = 20Unit price × quantity
Why it works
The unit price is the total cost divided by the number of items, and the cost of any number of items is that unit price times the number of items.
Common mistakes
- Multiplying 12 by 5 and treating the total price as the price of one pen.
- Dividing 12 by 5 instead of by the 3 pens that the 12 yuan actually buys.