The PEFRs of a group of 11-year-old girls follow a Normal distribution with mean 300 l/min and a standard deviation 20 l/min: (a) about 95% of the girls have PEFR between 260 and 340 l/min; (b) 50% of...

The PEFRs of a group of 11-year-old girls follow a Normal distribution with mean 300 l/min and a standard deviation 20 l/min:

(a) about 95% of the girls have PEFR between 260 and 340 l/min;

(b) 50% of the girls have PEFR above 300 l/min;

(c) the girls have healthy lungs;

(d) about 5% of girls have PEFR below 260 l/min;

(e) all the PEFRs must be less than 340 l/min.