A visit must be of at least 56.33 minutes to put a shopper in the longest 20 percent.
Normal Probability Distribution
Problems of normal distributions can be solved using the z-score formula. In a set with mean [tex]\mu[/tex] and standard deviation [tex]\sigma[/tex], the z-score of a measure X is given by:
[tex]Z=\frac{X-\mu}{\sigma}[/tex]
How long must a visit be to put a shopper in the longest 20 percent?
Here [tex]\mu=41.8 , \sigma=17.3[/tex]
The 100-20=80th percentile, which is X when Z has p-value of 0.8, so Z=0.84
[tex]Z=\frac{X-\mu}{\sigma}[/tex]
[tex]0.84=\frac{X-41.8}{17.3}[/tex]
14.532=X-41.8
X=14.532+41.8
X=56.33
A visit must be of at least 56.33 minutes to put a shopper in the longest 20 percent.
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