From an urn containing 7 white and 3 green balls, 3 balls are drawn in succession, without replacing them. Construct the probability distribution of W, the number of white balls in the sample, then compute the mean and standard deviation of W.
I've created a tree diagram but I am confused as to how to calculate the mean and standard deviation.
mean=pr(oneW)*1 + pr(twoW)*2+ prd(three)*3
standard deviation
To calculate the standard deviation of those numbers:
1. Work out the Mean (the simple average of the numbers)
2. Then for each number: subtract the Mean and square the result.
3. Then work out the mean of those squared differences.
4. Take the square root of that and we are done!