The mechanical advantage of a machine is the ratio between the output force and the input force:
[tex]MA= \frac{F_O}{F_I} [/tex]
In our problem, the input force is 100 N, while the output force is the weight of the object the student lifts, 500 N. So, the mechanical advantage is
[tex]MA= \frac{500 N}{100 N}=5 [/tex]