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In a sustainable building project in Brisbane, a mixture of recycled concrete and new aggregate is used in a ratio of 3 : 5 by mass. The total mass of the mixture used for a foundation slab is 480 kg.
What is the exact mass, in kilograms, of the recycled concrete used? Express your answer as an exact fraction or whole number.
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- The ratio of recycled concrete to new aggregate is 3 : 5 by mass, meaning for every 3 parts recycled concrete, there are 5 parts new aggregate.
- The total number of parts in the mixture is 3 + 5 = 8 parts.
- The total mass of the mixture is 480 kg, which corresponds to 8 parts.
- To find the mass of one part, divide the total mass by the total number of parts: 480 kg ÷ 8 = 60 kg per part.
- The recycled concrete makes up 3 parts of the mixture.
- Multiply the mass per part by the number of parts for recycled concrete: 3 × 60 kg = 180 kg.
- The mass of recycled concrete used is therefore 180 kg.
- Check: 3 parts recycled concrete (180 kg) and 5 parts new aggregate (5 × 60 = 300 kg) sum to 180 + 300 = 480 kg, matching the total.
- Verify the ratio: 180 : 300 simplifies by dividing both by 60 to 3 : 5, which matches the given ratio.
Reference answer: 180 kg
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