Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Normal Distribution help

  1. Apr 25, 2010 #1
    If anyone could help me with the following Q it would be much appreciated!

    Womens weights - N (68kg, (18)^2 kg) Mens Weights - N (82kg, (15)^2 kg)
    Mary and Jon are sailing a raft. Marys equipment weights 20% of her weight. Jons weighs 50% of his weight. The raft will sink if the total weight is greater than 170kg.
    Compute the probability that they make it home safely. (assume weights of mary and jon are sampled independantly from the relevant distributions?

    I am having trouble with how to combine the standard deviations etc. Please help!
     
  2. jcsd
  3. May 9, 2010 #2

    EnumaElish

    User Avatar
    Science Advisor
    Homework Helper

    If x1 ~ N(m1, s12) and x2 ~ N(m2, s22) then ax1 + bx2 ~ N(am1+bm2, a2s12 + b2s22).

    Note, the unit of variance is not kg but kg2.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook