Pipe A can fill 350 litres in \(3\frac{1}{2}\) minutes and pipe B can fill 780 litres in \(8\frac{2}{3}\) minutes. How long will both pipes together take to fill 1615 litres?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \(8\frac{1}{2}\) min
Find each pipe's rate in litres per minute; pipes filling together add their rates.
Rate of A \(\displaystyle =350\div\frac{7}{2}=100\) litres per minute
Rate of B \(\displaystyle =780\div\frac{26}{3}=90\) litres per minute
Together \(=100+90=190\) litres per minute
Time \(\displaystyle =\frac{1615}{190}=8.5=8\frac{1}{2}\) minutes