18. Let the random variable

*X*represent the profit made on a randomly selected day by a small clothing store on Main Street. Assume*X*is normal with a mean of $360 and a standard deviation of $50. | What is P(X > $400)? | |||

A) | 0.2119 | C) | 0.7881 | |

B) | 0.2881 | D) | 0.8450 | |

Answer: | A | |||

Topic: | 4.3 Random Variables | |||

You know that X, the random variable is normally distributed. So you can use the Excel = normdist function. Note that we want X

**greater than $400**. So we are looking for the area to the**right o**f X=400. Because Excel ‘adds up’ from left to right, that means we will have to calculate the area up to 400, and then subtract from 1. You can do all this in one go with=1-normdist(400,360,50,true). That gives 0.211855 which you can round up to get the answer in A.

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