<prompt> The PEFR of a group of 11 year old girls follow a normal distrubution with mean 300 1min and standard detion 20 limin -About 95 of the girls have PEFR between 260 and 340 1min.The girls have healthy lungsAbout 5 of girls have PEFR below 260 1min.All the PEFR must be less than 340 1min  <response>: Ans. is a i.e., About 95 of the girls have PEFR between 260 and 340 1min o 1 SD includes -- 68 of values o 2 SD includes -- 95 of values o 3 SD includes -- 99.7 of values In this question Mean PEFR 300 Lmin SD 2 Lmin i Area around 1 SD on either side of mean x 1 SD will include 68 of values, i.e. x-1SD300-20 So, 68 of girls have PEFR between 280 320 Lmin. ii Area around 2SD on either side of mean x 2SD will include 95 of values, i.e. x 2SD300-40 So, 95 of girls have PEFR between 260 340 Lmin. iii Area around 3SD on either side of mean x 3SD will include 99.7 of values, i.e. - x-3SD 300 60 So, 99.7 ofgirls will have PEFR between 240 360 Lmin. 