Social & Preventive Medicine The PEFR of a group of 11 year old girls follow a normal distribution with mean 300 l/min and standard detion 20 l/min : A About 95% of the girls have PEFR between 260 and 340 l/min B The girls have healthy lungs C About 5% of girls have PEFR below 260 l/min D All the PEFR must be less than 340 1/min 💡 Explanation The PEFR of a group of 11 year old girls follow a normal distribution with mean 300 l/min and standard detion 20 l/min : ✓ Correct Answer: A. About 95% of the girls have PEFR between 260 and 340 l/min