The following table is a probability distribution of the amount of time required to evacuate the low-lying areas of the Gulf Coast in the event of a hurricane. Time to evaccuate 13 14 15 16 17 18 - (in hours) Probability 0.04 0.25 0.40 0.18 0.10 0.03 a) Let X be the random variable 'time to evacuate in hours'. Compute E(X) by hand. b) c) Compute Var(X) by hand. Compute the standard deviation of X
Continuous Probability Distributions
Probability distributions are of two types, which are continuous probability distributions and discrete probability distributions. A continuous probability distribution contains an infinite number of values. For example, if time is infinite: you could count from 0 to a trillion seconds, billion seconds, so on indefinitely. A discrete probability distribution consists of only a countable set of possible values.
Normal Distribution
Suppose we had to design a bathroom weighing scale, how would we decide what should be the range of the weighing machine? Would we take the highest recorded human weight in history and use that as the upper limit for our weighing scale? This may not be a great idea as the sensitivity of the scale would get reduced if the range is too large. At the same time, if we keep the upper limit too low, it may not be usable for a large percentage of the population!
![The following table is a probability distribution of the amount of time required to evacuate the low-lying
areas of the Gulf Coast in the event of a hurricane,
Time to evacuate 13
- (in hours)
Probability
14
15
16
17
18
0.04 0.25 0.40 0.18 0.10 0.03
a)
Let X be the random variable 'time to evacúate in hours'. Compute E(X) by hand.
b)
c)
Compute Var(X) by hand.
Compute the standard deviation of X
d)
Does this data appear to be normal? Explain.
Assuming the data is normal, and use the answers from above to compute the probability
that the time to evacuate will be less than or equal to 14 hours,
e)
Scientists cannot predict when and where a hurricane will make landfall more than
14 hours in advance. If the government waits to evacuate when they get a prediction
from the scientists, what is the probability that the area will be evacuated safely?
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