A manufacturer has agreed to dispatch small servomechanisms in cartons of 100 to a distributor. The distributor requires that 90% of cartons contain at most one defective servomechanism. Assuming the Poisson approximation to the binomial distribution, write down an equation for the Poisson parameter l such that the distributor’s requirements are just satisfied. Solve by trial and error (approximate solution 0.5), and hence find the required proportion of manufactured servomechanisms that must be satisfactory.