SOLUTION: The amount of Jen's monthly phone bill is normally distributed with a mean of $50 and a standard deviation of $9. What percentage of her phone bills are between $23 and $77?
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Question 1161649: The amount of Jen's monthly phone bill is normally distributed with a mean of $50 and a standard deviation of $9. What percentage of her phone bills are between $23 and $77? Answer by Boreal(15235) (Show Source):
You can put this solution on YOUR website! z=(x-mean)/sd
for $23
z=(23-50/9=-3
and
z=(77-50)/9=+3
probability of z between -3 and +3 is about 99.7%.
