Question

A pipe can empty a tank in 40 minutes. A second pipe with diameter twice as much as that of the first is also attached with the tank to empty it. The two together can empty the tank in 

(a) 8 min 

(b) \(13\frac{1}{3}\) min 

(c) 30 min 

(d) 38 min

Answer 1

(b) 13\(\frac{1}{3}\) min

A pipe with double the diameter can empty a tank in half the time, i.e., in 20 min.

\(\therefore\) Part of the tank emptied by the two pipes together 

= \(\big(\frac{1}{40}+\frac{1}{20}\big)\) = \(\frac{1+2}{40}\) = \(\frac{3}{40}\)

\(\therefore\) The tank will be emptied by the two pipes together in \(\frac{40}{3}\) min. = \(13\frac{1}{3}\)  min.