random variable with normal distribution

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Tony
Tony 2013-11-11
回答： Roger Stafford 2013-11-11
Hello, here is the problem:
A random variable obeys a normal distribution. It has a mean value equal to 100 and a standard deviation equal to 3. Find the probability that:
x < 98
98 < x < 104
x > 98
I have a slight idea i know how to find mean using mean(x) and randn(x) for some random number but no idea how to tie them together.
thank you for your time

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回答（3 个）

Matt J
Matt J 2013-11-11
See the erf() command.
Image Analyst
Image Analyst 2013-11-11
If you want to do it empirically (like Monte Carlo), you can use this:
numberOfNumbers = 1000000; % Whatever number you want.
% From the help:
randomNumbers = 100 + 3 * randn(1, numberOfNumbers);
% Count number less than 98
count = sum(randomNumbers < 98)
fprintf('The number of numbers less than 98 = %g%%\n',...
count * 100 / numberOfNumbers);
Repeat for other ranges.
Roger Stafford
Roger Stafford 2013-11-11
The Statistics Toolbox function 'normcdf' is just what you need.

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