Suppose the amount of light (in lumens) emitted by a particular brand of 40W light bulbs is normally distributed with a mean of 450 lumens and a standard deviation of 20 lumens.

What percentage of bulbs emit between 425 and 475 lumens? (Show all of the calculations.)

(a) Draw a sketch of the normal curve and shade the desired area.

(b) Calculate the corresponding z values.

(c) Find the corresponding area under the standard normal curve.

(d) Interpret the final answer.