In: Statistics and Probability
Milk Demand
A supermarket has determined that daily demand for milk containers
has an approximate bell shaped distribution, with a mean of 55
containers and a standard deviation of six containers.
What percentage of the time will the number of containers of milk
sold within 2 standard deviations from the mean?
Solution:
Given, an approximate bell shaped distribution (Normal distribution) with,
= 55
= 6
* Using Empirical Rule
According to the empirical rule , 68% of the data lie within 1 standard deviations from the mean ,
95% of the data lie within 2 standard deviations from the mean , 99.7% of the data lie within 3 standard deviations from the mean.
So , answer is 95%
* Using Z transformation
P(within 2 standard deviations)
= P[ ( - 2) < X < ( + 2) ]
= P[ (55 - 2*6) < X < (55 + 2*6)]
= P[ (55 - 12) < X < (55 + 12)]
= P[43 < X < 67]
= P(X < 67) - P(X < 43)
= P[(X - )/ < (67 - 55)/6] - P[(X - )/ < (43 - 55)/6]
= P[Z < 2.00] - P[Z < -2.00]
= 0.9772 - 0.0228..Use z table
= 0.9544
= 95.44% or nearly 95%