Pipe A can fill 240 litres in \(2\frac{2}{5}\) minutes and pipe B can fill 450 litres in \(7\frac{1}{2}\) minutes. How long will both pipes together take to fill 1240 litres?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \(7\frac{3}{4}\) min
Find each pipe's rate in litres per minute; pipes filling together add their rates.
Rate of A \(\displaystyle =240\div\frac{12}{5}=100\) litres per minute
Rate of B \(\displaystyle =450\div\frac{15}{2}=60\) litres per minute
Together \(=100+60=160\) litres per minute
Time \(\displaystyle =\frac{1240}{160}=7.75=7\frac{3}{4}\) minutes