# The expected (mean) life of a particular type of light bulb is 1000 hours with a standard deviation of 50 hours. The life of this bulb is normally…

1.

The expected (mean) life of a particular type of light bulb is 1000 hours with a standard deviation of 50 hours. The life of this bulb is normally distributed.

**What is the probability that a randomly selected bulb would last longer than 1150 hours?**

2. The average hourly wage of workers at a fast food restaurant is $6.50/hr with a standard deviation of $0.45. Assume that the distribution is normally distributed. If a worker at this fast food restaurant is selected at random, **what is the probability that the worker earns more than $6.75?**

3.

Let X be a normal random variable with mean 20 and standard deviation 4.

**The 90th percentile of X is ____________.**

4. For a normal distribution with mean –15 and standard deviation 6, the value –24 has a z value of:

5. The mean weight of loads of rock is 46.0 tons with a standard deviation of 8.0 tons. If 25 loads are chosen at random for a weight check, find the probability that the mean weight of those loads is less than 44.24 tons. Assume that the variable is normally distributed.

6.

Suppose X is a normal random variable with mean 60 and standard deviation 2. A z-score was calculated for a number, and the z-score is 3.4.

**What is x?**

7. Give the term for the number of standard deviations that a particular X value is away from the mean.

8.

Let Z be a normal random variable with mean 0 and standard deviation 1.

**Use the normal tables to find P(1.3 < Z < 2.3).**