In 1 of every 5 bars of 'Choco Fudge', a chocolate bar costing 30p, is a coupon which can be traded in for a toy car at any shop which sells them. Kenny is set on having one of these toy cars but he doesn't have enough pocket money to buy any of the bars. His father says that if he can tell him how much it would cost to buy just enough bars for there to be at least a 90% chance of him getting a coupon, he'll give Kenny the money to buy the toy car. But he can't figure it out.

Help Kenny get his toy car by posting the answer in this thread!