Hi All

Wonder if you can help. I apologise if this is basic but I am just learning Statistics and using the Khan Academy courses. I am a bit stuck when it comes to combining random variables. According to what I understand, you can add the means of 2 distributions and add the variances. However, if I produce small test distributions, I can show this doesn't work. For example:

Distribution A: 4,4,5,5,6,6,6,7 mean = 5.375 variance = 0.9844

Distribution B: 4,,5,5,5,5,7 mean = 5.167 variance = 0.8055

So based on what I have read, the combined mean should be 10.542, combined variance should be 1.7899

However, if I create Distribution C, by combining the values in A and B, I get 4,4,4,5,5,5,5,5,5,6,6,6,7,7 with mean 5.2857 and variance of 0.9183

So is my understanding incorrect that combining random variables is the same as combining the values into one distribution?

thanks

Matt

Wonder if you can help. I apologise if this is basic but I am just learning Statistics and using the Khan Academy courses. I am a bit stuck when it comes to combining random variables. According to what I understand, you can add the means of 2 distributions and add the variances. However, if I produce small test distributions, I can show this doesn't work. For example:

Distribution A: 4,4,5,5,6,6,6,7 mean = 5.375 variance = 0.9844

Distribution B: 4,,5,5,5,5,7 mean = 5.167 variance = 0.8055

So based on what I have read, the combined mean should be 10.542, combined variance should be 1.7899

However, if I create Distribution C, by combining the values in A and B, I get 4,4,4,5,5,5,5,5,5,6,6,6,7,7 with mean 5.2857 and variance of 0.9183

So is my understanding incorrect that combining random variables is the same as combining the values into one distribution?

thanks

Matt

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