04 Try it yourself Interactive

Work out when to shut the pipe

Pipe A is the one that gets closed and pipe B stays open throughout. Choose their solo times and the total time the tank must be full in, and each step builds one term of the subtraction. Push the target time outside its feasible window and the solver refuses, with the window printed out.

A 25 h, B 20 h, full in 12 h
close A after 10 h
With A at 25 and B at 20, try a target of 20 hours. B alone already manages that, so there is nothing left for A to do and no sensible closing time.
Press Next to work through it one step at a time.
Tank units–
B delivers–
Left for A–
Close A at–
step 0 / 0