SOLUTION: The customer accounts at a certain departmental store have an average balance of Shs.480 and a standard deviation of Shs.160. Assuming that the account balances are normally distri

Algebra ->  Probability-and-statistics -> SOLUTION: The customer accounts at a certain departmental store have an average balance of Shs.480 and a standard deviation of Shs.160. Assuming that the account balances are normally distri      Log On


   

Question 1150436: The customer accounts at a certain departmental store have an average balance of Shs.480 and a standard deviation of Shs.160. Assuming that the account balances are normally distributed
i)What proportion of the accounts is over Shs.600? (2 marks)
ii)What proportion of the accounts is between Shs.400 and Shs.600 (2 marks)
iii) What proportion of the accounts is between Shs.240 and Shs.360 (2 marks)
Answer by Glaviolette(140) About Me  (Show Source):
You can put this solution on YOUR website!
i) z = (600-480)/160 = 0.75
From z-table, P(>Shs.600) = 1 - 0.7734 = 0.2266
ii) z = (400-480)/160 = -0.5
Using previous answer and area for z = -0.5 (0.3085), P(Shs.400 iii) z = (240-480)/160 = -1.5
z = (360-480)/160) = -0.75
P(Shs.240