A car showroom sells cars at a steady rate of 1 per day. When its stock gets down to 6 it takes delivery of another 20 cars. This policy has been going on for some time, but having expanded the showroom the management decide they will take delivery of 30 cars whenever the stock gets down to 10. They still expect to sell 1 car per day.

How will the average number of cars in the showroom between deliveries change compared with the average under the old policy?