3 kg of oranges cost 24 yuan: price of 7 kg?

At a fruit shop, 3 kg of oranges cost 24 yuan in total. At the same unit price, how much do 7 kg of oranges cost?

Step-by-step

1. 24 ÷ 3 = 8
   Find the unit price first (reduce to one)
2. 8 × 7 = 56
   Unit 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 24 by 7 to get the price per kilogram.
• Adding 8 to 24 after finding 8 yuan per kilogram instead of multiplying 8 by 7.

Related

meeting-problem dice-probability unitary-notebooks-4-for-20