A block and tackle are made up of multiple pulleys, some of them fixed and some movable.The number of weight supporting ropes determines the mechanical advantage of a block and tackle, so in this case, the mechanical advantage is four.Viewing the figure from right to left, notice there are four ropes supporting the weight and a fifth rope where the effort is applied.In Figure below, the block and tackle are made up of four pulleys, the top two being fixed and the bottom two being movable.If the weight were 200 lb, it would require a 50 lb effort to lift it.