Let X be the number of cell phone minutes used by high school seniors.
X follows Normal distribution with mean μ = 500 and standard deviation σ =50.
The probability that students uses between 400 and 500 minutes is
P(400 < X < 500) = [tex] P(\frac{400-500}{50} < \frac{x -mean}{standard deviation} < \frac{500-500}{50} )
[/tex]
= P( -2 < Z < 0)
= P(Z < 0) - P(Z < -2)
= 0.5 - 0.0228
P(400 < X < 500) = 0.4772
The probability that student uses between 400 and 500 minutes is 0.4772
