Pipe A fills a tank in 20 hours and pipe B fills the same tank in 30 hours. How long will they take to fill the tank together?
Answer and explanation
Correct answer: B. 12 hours
- Step 1: In one hour A fills 1/20 of the tank and B fills 1/30.
- Step 2: Together 1/20 + 1/30 = 50/600 per hour, so the time is 600/50 = 12 hours.
Answer
12 hours.
Why not the others: 25 hours: the times were averaged. 50 hours: the times were added. 10 hours: the times were subtracted.
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