Now, there are 6 students who are sharing 4 desks at the library. While 4 of them are using the desks, the other 2 students have to wait and watch. If they have to use the desk for the same amount of time, how long does each of time can use the desk within 5 hours?
I solve like this, let each student uses $x$ min $$\frac{4}{6}=\frac{x}{300}$$
So, each student uses 200 min while each of them need to wait for 100 min.
I am wondering if I am correct to set the equation. Thanks a lot.