The PEFR of a group of 11 year old girls follow a normal distribution with mean 300 L/min and stardard detion 20 L/min-
About 95 % of the girls have PEFR between 260 and 340 L\/min The girls have healthy lungs About 5% of girls have PEFR below 260 L\/min All the PEFR must be less than 340 L\/min