SPM – MCQ 103 – Statistics

The PEFR of a group of 11 year old girls follow a normal distribution with mean 300 l/min and standard deviation 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 l/min

Correct answer : A. About 95% of the girls have PEFR between 260 and 340 l/min

  • 95.4% of values lie within 2 SD (standard deviation) of the mean
  • Here, SD = 20 l/min
  • Hence 95.4% of values lie within 300-(2*20) and 300=(2*20)
  • Which translates into : About 95% of the girls have PEFR between 260 and 340 l/min

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