A ski resort is planning a year-end promotion by offering a weekend special for $159 per person based on double occupancy. The high season rate for these rooms, which includes lift tickets, normally is $299. Management wants to hold some rooms for late arrivals who are willing to pay the season rate. If the number of skiers who are willing to pay full rate has a normal distribution with a mean of 50 and a standard deviation of 10, how many rooms should be set aside for full-paying skiers?