Question

If a machine gives you a mechanical advantage of 4 and a force output of 10, what must the force input be?

Answer 1

Use common sense on this. Think of a car jack. If you have a jack handle and it has a mechanical advantage of 4, and you want to lift 10 kg, then the force you have to put on the handle to raise that 10 kg is going to be 4 times easier...:
!0 / 4 = 2.5 force input