SOLUTION: Old Faithful geyser in Yellowstone National Park has a mean time between eruptions of 85 minutes. If the interval of time between eruptions follows a normal distribution with stan

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Question 1197760: Old Faithful geyser in Yellowstone National Park has a mean time between eruptions of 85 minutes. If the interval of time between eruptions follows a normal distribution with standard deviation 21.25 minutes, what is the probability that a random sample of 32 time intervals between eruptions has a mean longer than 87 minutes? Include four digits after the decimal.
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!

Hi  
Normal Distribution: µ = 85 and σ = 21.25
n = 32  (NOte:  Sample Size > 30)
Using TI or similarly an inexpensive calculator like an Casio fx-115 ES plus
P(x > 87) =  normcdf( 87, 9999,  85, 21.25/√32) =+.2972
Or
 z+=blue+%2887+-+85%29%2Fblue%2821.25%2Fsqrt%2832%29%29=  = .5324
 1- P( z ≤.5324) = 1- .7027 = .2972
    
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