text: # Gaussian Distribution
  
  • Apr 17th 2007, 03:09 PM
  thefirsthokage
  Gaussian Distribution
  The strength levels of a group of Martians follows Normal distribution with a mean of 75kgf and a std. dev. of 5kgf.
  
  (a) How many Martians do you expect to meet before you find one with a strength level greater than 72 kgf?
  
  (b) In a group of 5 Martians, what is the probability that exactly 4 Martians have strength levels greater than 72 kgf?
  
  (c) 4 Martians are trying to open a huge stone door which will open only if all of their individual strength levels are greater than 72 kgf. What is the probability that they will open the door?
  
  EDIT: Never mind I figured out (a) and (c). Still need help on (b), though. Thanks. I'll probably kick myself for not seeing it, but oh well.
  • Apr 27th 2007, 12:42 PM
  CaptainBlack
  Quote:
  
  Originally Posted by thefirsthokage
  The strength levels of a group of Martians follows Normal distribution with a mean of 75kgf and a std. dev. of 5kgf.
  
  (a) How many Martians do you expect to meet before you find one with a strength level greater than 72 kgf?
  
  (b) In a group of 5 Martians, what is the probability that exactly 4 Martians have strength levels greater than 72 kgf?
  
  (c) 4 Martians are trying to open a huge stone door which will open only if all of their individual strength levels are greater than 72 kgf. What is the probability that they will open the door?
  
  EDIT: Never mind I figured out (a) and (c). Still need help on (b), though. Thanks. I'll probably kick myself for not seeing it, but oh well.
  
  Calculate the probability p(72) that a martian has strength > 72 kgf. Then
  the number with strength >72 kgf in a sample of 5 has a binomial distribution
  B(p(72), 5). So prob of 4 having strength >72 kgf is b(4, p(72), 5).
  
  RonL