Jessicaaaa11
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A study showed that the time, T minutes, spent by a customer between entering and leaving Fely's department store has a mean of 20 with a standard deviation of 6.
Assume that T may be modelled by a normal distribution.
a.) find the value of T exceeded by 20% of customers
b.) i.) write down the standard deviation of the mean time spent in Fely's store by a random sample of 90 customers
ii.) find the probablilty that this mean time will exceed 21 minutes
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Bobjim12
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a you make 20% 0.2
b. dunno
c. standardise it.
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Jessicaaaa11
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So find 0.2 on the tables?
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Kevin De Bruyne
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(Original post by Jessicaaaa11)
A study showed that the time, T minutes, spent by a customer between entering and leaving Fely's department store has a mean of 20 with a standard deviation of 6.
Assume that T may be modelled by a normal distribution.
a.) find the value of T exceeded by 20% of customers
b.) i.) write down the standard deviation of the mean time spent in Fely's store by a random sample of 90 customers
ii.) find the probablilty that this mean time will exceed 21 minutes
If 20% of customers exceed a certain value what percent gets less than or equal to that value? What does that say about the probability of T being less than or equal to that value?

How do you work out the variance/standard deviation of the mean?
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