Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability and convert it to standard deviations.
For example: P < .2 is approximately -.84 SD.
Continue with your other data.
The random variable X follows normal distribution.P(X<35)=0.2 and P(35<X<45)=0.65.Find mean and standard deviation.
Answer as fast as possible.
3 answers
Again using
http://davidmlane.com/normal.html
with setting on "value from an area"
if P(X<35)=0.2 and P(35<X<45)=0.65 then P(x<45) = .85
entering .2 and clicking below gave me a z-score of -.841
(35-m)/s = -.841 ---> m - .841s = 35
entering .85 and clicking below gave me a z-score of 1.036
(45-m)/s = 1.036 ----> m + 1.036s = 45
subtract those two equations:
1.877s = 10
s = 5.3277
m = 39.48
http://davidmlane.com/normal.html
with setting on "value from an area"
if P(X<35)=0.2 and P(35<X<45)=0.65 then P(x<45) = .85
entering .2 and clicking below gave me a z-score of -.841
(35-m)/s = -.841 ---> m - .841s = 35
entering .85 and clicking below gave me a z-score of 1.036
(45-m)/s = 1.036 ----> m + 1.036s = 45
subtract those two equations:
1.877s = 10
s = 5.3277
m = 39.48
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3 answers