In: Statistics and Probability
Use the empirical rule to solve the problem. The amount of jen's monthly phone bill is normally distributed with a mean of $55 and a standard deviation of $12. What percentage of her phone bills are between $19 and $9?
SOLUTION:
From given data,
Use the empirical rule to solve the problem. The amount of jen's monthly phone bill is normally distributed with a mean of $55 and a standard deviation of $12. What percentage of her phone bills are between $19 and $9
mean = = 55
standard deviation = =12
Let, a random variable X denotes the amount of jen's monthly phone bill (In $)
& X N ($55 , ($12)2)
Let ,
z = (x-) / N (0,1)
We have to find percentage of her phone bill are between $19 and $9
P(19 < x < 9) = P(19- / < x - / < 9- / )
= P(19- 55 /12 < Z < 9- 55 /12 )
= P(-3 < Z < -3.83 )
= P(Z < -3.83 ) - P(Z < -3 )
= 0.00006-0.00135
= -0.00129
The percentage of jen's phone bills are between $19 and $9 is
= 100*(-0.00129)
= - 0.129 %