<prompt> The PEFR of a group of 11 year old girls follow a normal distribution with mean 300 Lmin and stardard detion 20 Lmin-About 95 of the girls have PEFR between 260 and 340 LminThe girls have healthy lungsAbout 5 of girls have PEFR below 260 LminAll the PEFR must be less than 340 Lmin  <response>: Ref:Parks 23rd edition pg 849. SD 1 : confidence limit 68 SD 2 : confidence limit 95 SD 3 : confidence limit 99.7 Here 2SD 2x20 -40 So, between 260 and 340 2SD covers 95 values, remaining is 5, So 5 fall below 260 and above 340 Precisely 2.5 below 260 and 2.5 above 340 