A high school sell their footballs headbands for $0.50. Each headband costs the high school $0.20 to buy from the manufacture. The local recycling center will pay you $0.10 per headband that is unsold at the end of the day. Demand for the headbands follows a normal distribution with mean equals to 100 and standard deviation equals to 20. How many headbands should be ordered? What is the probability of stock-out?