Tim Worker is doing his budget. He discovers that the average electric bill for the year was $206 with a standard deviation of $10.00. What percent of his expenses in this category would he expect to fall between $184.00 and $200.00? The z for $184.00 = - .62.22 . The percent of area associated with $184.00 = 62.2 %. The z for $200 = - .622.22 . The percent of area associated with $200 = 48.6 %. Subtracting the two percentages, the percent of expenses between $184.00 and $200.00 is 622.22
Accepted Solution
A:
We use the z score formula:
z = (x β u) / s
Β
Find z at x = 184 and x = 200 then use the standard
tables to find for the P value using right tailed test.
Β
at x1 = 184
z1 = (184 β 206) / 10 = -2.20
From the tables, P1 = 0.9861
Β
at x2 = 200
z2 = (200 β 206) / 10 = -0.60
From the tables, P2 = 0.7257
Β
So the probability it falls from 184 to 200 is:
P = 0.9861 β 0.7257
P = 0.2604Β