SECTION B The speeds of cars passing a certain point on a motorway can be taken to be normally distributed. Observations show that of cars passing the point, 95% are travelling at less than 85 m.p.h. and 10% are travelling at less than 55 m.p.h. (a) Find the average speed of the cars passing the point. (b) Find the proportion of cars that travel at more than 70 m.p.h