Posted by Tracy on Saturday, March 29, 2014 at 10:00am.
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, Saturday, March 29, 2014 at 10:16am
http://davidmlane.com/hyperstat/z_table.html

Stats  Tracy, Saturday, March 29, 2014 at 12:42pm
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, Saturday, March 29, 2014 at 12:43pm
These are my options.
A.0.30
B.0.40
C.0.60
D.0.90

Stats  Steve, Saturday, March 29, 2014 at 4:56pm
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)
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