A large water tank has two inlet pipes (a large and a small one) and one outlet pipe. It takes 2
hours to fill the tank with the large inlet pipe. On the other hand, it takes
5
hours to fill the tank with the small inlet pipe. The outlet pipe allows the full tank to be emptied in
7
hours. Assuming that the tank is initially empty, what fraction will be filled in
1
hour if all three pipes are in operation? Your answer should be a fraction in simplest form, without spaces, e. g. 1/2.