Ahmad mixes sand, cement, and water in the ratio 3 : 2 : 5 by volume. He has exactly 12 litres of cement and uses it all. After mixing, he pours out 1/4 of the total mixture. How many litres of sand remain in the mixture?
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Worked Solution
Step 1: Ratio sand : cement : water = 3 : 2 : 5. Cement = 2 parts = 12 L → 1 part = 6 L.
Step 2: Sand = 3 × 6 = 18 L. Water = 5 × 6 = 30 L. Total mixture = 60 L.
Step 3: Ahmad pours out 1/4 of the total: volume poured = (1/4) × 60 = 15 L.
Step 4: Sand is 3/10 of the mixture. Sand poured out = (3/10) × 15 = 4.5 L.
Alternatively: Sand remaining = (3/4) × 18 = 13.5 L.
Step 5: Sand remaining = 18 − 4.5 = 13.5 litres.
Correct answer: 13.5
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