Question

According to cbs money watch, the average monthly household cellular phone bill is $100. suppose monthly household cell phone bills are normally distributed with a standard deviation of $11.35.
a. what is the probability that a randomly selected monthly cell phone bill is more than $127

Answer 1

The probability that a randomly selected monthly cell phone bill is more than $127 is given by

$P(X\ \textgreater \ 127)=1-P(X\ \textless \ 127) \\ \\ =1-P\left(z\ \textless \ \frac{127-100}{11.35} \right)=1-P(z\ \textless \ 2.38) \\ \\ =1-0.99132=0.00868$