The diagram of a single fixed pulley is shown alongside. If T is the tension in each strand of the string and in the ideal case string is massless and there is no friction in the pulley bearings, then in equilibrium, E = T and L = T
(i) Mechanical advantage = L/E = T/T = 1
(ii) If the effort E moves a distance d downwards, the load L moves the same distance d upwards.
So, velocity ratio = dE/dL = d/d = 1
(iii) Efficiency = M.A./V.R. = 1/1 = 1(or 100%).