Statistics
posted by LT on .
1) Find the missing parameter
1.mean 15, 30.15 %, above 50; what is the standard deviation
2.mean 75, 5.05% below 30; what is the standard deviation
3.standard deviation 9, 85.08% below 105: what is the mean
4.standard deviation 16.8, 15.62% above 18.3: what is the mean

Z = (raw score  mean)/standard deviation
Look up the percentage in a table in the back of your stat text labeled something like "areas under a normal distribution" to get your Z score value.
Insert the values into the equation above and solve for the unknown.
I hope this helps. Thanks for asking. 
what is the probabilty of a sample of 25 houses will be tetween 145 and 160 days