Pipes and Cisterns Practice Test 1 with solutions

In 1 minute the part filled by all the three pipes = $\frac{1}{4}+\frac{1}{5}-\frac{1}{3}$ = $\frac{7}{60}$
Hence, all the three pipes will fill the tank in $\frac{60}{7}$ minutes.
Since, 4/5 th the full tank can be filled by all the three pipes in $\frac{4}{5}\times \frac{60}{7}$ = $\frac{48}{7}$ = $6\frac{6}{7}$ minutes.