AlgebraHardTwo pipes filling a tank
Algebra practice question
One pipe can fill a tank in 6 hours, and a second pipe can fill it in 3 hours. If both pipes are used together, how many hours does it take to fill the tank?
Answer: 2
Rates: 1/6 + 1/3 = 1/2 of the tank per hour, so the tank fills in 2 hours.
Common wrong answers
- If you answered 3
- 3 is the faster pipe alone; adding the other must reduce the time.
- If you answered 9
- 9 adds the times; together they must be faster than either alone.
- If you answered 4.5
- 4.5 averages the two times, which is not how rates combine.
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