One pipe fills a barrel in 3 hours and another pipe fills it in 6 hours. How many hours does it take to fill the barrel when both pipes are open?

Answer and explanation

Correct answer: C.

  1. Step 1: Rates add: of the tank per hour. Step 2. Time hours. **Answer: . Why not the others:** averages the two times; adds the two times; subtracts the times.

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