Question

Water needs to be removed from an underground chamber before work can commence. When the water was at a depth of 3m, five suction pipes were used and emptied the chamber in 4 hours. If the water is now at a depth of 5m (same cross-section), and you want to empty the chamber in 10 hours time, how many pipes need to be used?

Answer 1

We would need to use 4 pipes to be sure to empty the chamber within 10 hours time. 

Work: 
5*5/3*4/10=3 1/3 pipes (but we must round since we cant have 1/3 of a pipe running. This means that we must have 4 pipes.