It took longer, A couple of minutes, to remember the principle and then through the equation solved.
One fills the pool in 30 minutes. second in 45 minutes, third for 90 minutes. How much will they all fill the pool together??
China buys copper from 150 to 400 behind 2 of the year, India for 3 of the year. How much will they take copper to 1000 ? :))