1. Assume blood pressure readings are normally distributed with a mean of 120 and standard deviation of 8. What percentage of people have a blood pressure reading greater than 145?

2. Assume that the salaries of elementary school teachers in the United States are normally distributed with a mean of $41,000 and a standard deviation of$4,000. What is the cut-off salary for teachers in the bottom 10%?

I greatly appreciate any one's help. These are problems I have struggled with this semester....and now that the end is winding down I would love to figure them out for future references. Thank so much to everyone!

2. Originally Posted by loutja35
1. Assume blood pressure readings are normally distributed with a mean of 120 and standard deviation of 8. What percentage of people have a blood pressure reading greater than 145?

2. Assume that the salaries of elementary school teachers in the United States are normally distributed with a mean of $41,000 and a standard deviation of$4,000. What is the cut-off salary for teachers in the bottom 10%?

I greatly appreciate any one's help. These are problems I have struggled with this semester....and now that the end is winding down I would love to figure them out for future references. Thank so much to everyone!
1. $\displaystyle \Pr(X > 145) = \Pr\left(Z > \frac{25}{8} \right) = 1 - \Pr\left(Z < \frac{25}{8} \right)$. The value of Z is found from $\displaystyle Z = \frac{X - \mu}{\sigma}$. You should have been taught how to calculate probabilities from a standard normal distribution.

2. Calculate the value of z* such that $\displaystyle \Pr(Z < z^*) = 0.1$. Then the cut-off salary, x*, is found from $\displaystyle z^* = \frac{x^* - 41,000}{4,000}$.

Note that z* is negative.

3. Originally Posted by loutja35
1. Assume blood pressure readings are normally distributed with a mean of 120 and standard deviation of 8. What percentage of people have a blood pressure reading greater than 145?
HI

$\displaystyle X - N (120 , 8^2)$

$\displaystyle P(X>145)=P(Z>\frac{145-120}{8})$

calculate this using the tables or calculator to get the probability , then convert it to percentage .