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Uniform Distribution

If a random variable XX follows a uniform distribution, its probability distribution (density) function is f(x)=1ba\boxed{\displaystyle f(x)=\frac{1}{b-a}}.

The probaiblity distribution (density) curve looks like this:
  • The curve is a flat line on the interval [a,b][a,b], where aa is the lowest possible value of XX and bb is the highest possible value of XX
  • The probability that the random variable takes on any value between x1x_1 and x2x_2 is the area of the rectangle under the curve, between x1x_1 and x2x_2
  • P(x1<X<x2)=(x2x1)×1baP(x_1<X<x_2)=(x_2-x_1)\times\frac{1}{b-a}
  • The mean of a uniform distribution is E(X)=μ=a+b2\boxed{E(X)=\mu=\frac{a+b}{2}}
  • This is the "middle" value of the interval
  • The standard deviation of the uniform distribution SD(X)=σ=(ba)212\boxed{\displaystyle SD(X)=\sigma=\sqrt{\frac{(b-a)^2}{12}}}

The time it takes for a golden retriever to fetch a stick is uniformly distributed between 8 seconds and 13 seconds.

a) What is the probability that she will take longer than 10 seconds the next time you throw a stick?

b) Find the mean of the uniform distribution.

c) Find the standard deviation of the uniform distribution.