A cereal company is putting 1 of 4 prizes in each box of cereal. The prizes are evenly distributed so the probability of winning any given prize is always 1 / 4. Vera wonders how many boxes she should expect to buy to get all 4 prizes. She carried out 36 trials of a simulation and her results are shown below. Each dot represents how many boxes it took to get all 4 prizes in that trial.