Mechanical advantage

What you put in is different than what comes out...

 

In a first class lever, the input force x the distance to the fulcrum + the resultant force x the distance to the fulcrum.  A 50kg.. force can balance a 150kg. person if the input is 3 m. from  the fulcrum and the output 1 m..(from the fulcrum).  This is a mechanical advantage of 150/50=3.