Question

A diving pool can be filled by a pipe in 10 hours if the drain is opened. If the pipe was allowed to run with the drain for 2 hours, and the drain is afterwards closed it would require the pipe 4 more hours to fill the tank. How long would it take the pipe to make the tank full if the drain is closed from the start?

Answer 1

if it takes 10 hours to fill when the drain is opened; then each hour the water runs with the drain open fills the pool by 10%

therefore after 2 hours the pool is at 20% capacity and the other 80% takes 4 hours to fill, which means while the drain is closed the pool fills at a rate of (80% / 4 hours) 20% every hour.

THEREFORE if it takes 20% per hour * 5 hours = 100% full to fill the pool with the drain closed.

Answer 2

Thank you! Its a big help :)