Social & Preventive Medicine The PEFR of a group of 11 year old girls follow a normal distrubution with mean 300 1/min and standard detion 20 limin – A About 95% of the girls have PEFR between 260 and 340 1/min. B The girls have healthy lungs C About 5% of girls have PEFR below 260 1/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 distrubution with mean 300 1/min and standard detion 20 limin - ✓ Correct Answer: A. About 95% of the girls have PEFR between 260 and 340 1/min.