Three pipes X, Y, and Z can fill a cistern in 10, 15, and 30 hours respectively. If all three pipes are opened together, how many hours will it take to fill the cistern completely?
Answer and explanation
Correct answer: C.
- Step 1: Rates per hour: , , .
- Step 2: Combined hourly rate: .
- Step 3: Total time to fill cistern: .
Answer
5.0 hours.
Why not the others: '' uses rates for two pipes; '' is an underestimate.
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