CalcElfCalcElf › 4 kg of rice cost 36 yuan: price of 9 kg?
4 kg of rice cost 36 yuan: price of 9 kg?
At a grain shop, 4 kg of rice cost 36 yuan in total. At the same unit price, how much do 9 kg of rice cost?
Answer
81
Step-by-step
- 36 ÷ 4 = 9Find the unit price first (reduce to one)
- 9 × 9 = 81Unit price × quantity
Why it works
The price of one kilogram is the total cost divided by the mass bought; when the unit price stays the same, the total cost grows in proportion to the mass.
Common mistakes
- Dividing 36 by 9 instead of by the 4 kg that were actually bought.
- Adding 9 to 36 after finding 9 yuan per kilogram instead of multiplying.