Pipe A fills a tank 1.5 times as fast as pipe B. Together the two pipes fill the empty tank in 12 hours. How long will pipe B alone take to fill the tank?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 30 hours
Let pipe B fill \(b\) part of the tank per hour. Then pipe A fills \(1.5b\) part per hour, and together they fill \(\frac{1}{12}\) per hour.
\(\displaystyle b + 1.5b = \frac{1}{12}\)
\(\displaystyle 2.5b = \frac{1}{12}\)
\(\displaystyle b = \frac{1}{30}\)
So pipe B alone takes 30 hours. (Pipe A alone takes \(30 \div 1.5 = 20\) hours.)