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A tap fills 36 litres of water in 4 minutes. How long will the same tap take to fill a 153-litre drum?

Class 7Comparing QuantitiesComparing Quantities
  • A4.25 minutes
  • B38 minutes
  • C17 minutes
  • D13 minutes

Step-by-Step Solution

Rate = litres per minute. Time for 153 litres = minutes. Check: . 13 minutes is the trap of filling only the remaining 153 − 36 = 117 litres and forgetting that the first 36 litres also take 4 minutes. 4.25 minutes divides 153 by 36, and 38 minutes divides 153 by 4 (about 38.25) — both divide by the wrong number instead of by the rate of 9 litres per minute.
Answer: C) 17 minutes

Key idea: Three forms of the same number

Fractions, decimals, and percentages are three notations for the same idea. Convert freely:

- **Fraction → percentage**: multiply by 100. .
- **Percentage → fraction**: divide by 100 and simplify. .
- **Decimal → percentage**: shift two places right. 0.34 = 34%.
- **Percentage → decimal**: shift two places left. 8% = 0.08.

With practice, this becomes automatic and you can move between forms without thinking.

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