Posted by Tracy on .
The high temperature X (in degrees Fahrenheit) on January days in Columbus, Ohio varies according to the Normal distribution with mean 21 and standard deviation 10.
The value of P(X < 10) is
 Stats  Damon,

Stats 
Tracy,
I added the mean of 21 and SD of 10 and the probability is 0.9715. That is not one of my options, please help!

Stats 
Tracy,
These are my options.
A.0.30
B.0.40
C.0.60
D.0.90 
Stats 
Steve,
Well, it must be immediately obvious that .9715 is bogus. A score of 10 is more than a whole SD below the mean, so there is no way that P(x<10) > 1/2
When I plugged in the data, I got P(x<10) = 0.1357
Still not one of your choices. However, the closest is 0.3, since you know that the score is well below the mean.
There's a typo somewhere in the problem or the answers.
I get
.30 = P(x<15 or x>26)
...
.90 = P(x<33 or x>8)