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Suppose you record how long it takes you to get to work or school over many...

Suppose you record how long it takes you to get to work or school over many months and discover that the times are approximately bell-shaped with a mean of 16 minutes and a standard deviation of 2 minutes. How much time (in minutes) should you allow to get there to make sure you are on time 80% of the time
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Answer #1

X ~ N ( µ = 16 , σ = 2 )
P ( X < ? ) = 80% = 0.8
Looking for the probability 0.8 in standard normal table to calculate critical value Z = 0.84
Z = ( X - µ ) / σ
0.84 = ( X - 16 ) / 2
X = 17.68
P ( X < 17.68 ) = 0.8

You should allow 17.68 minute to make sure you are on time 80% of the time.

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