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# Rules for Variance

1. The variance of a constant is zero.
2. Adding a constant value, c to a variable does not change variance (because the expectation increases by the same amount).
3. Multiplying a constant value, c to a variable increase the variance by square of the constant, c.
4. The variance of the sum of two or more random variables is equal to the sum of each of their variances only when the random variables are independent.

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# Rules for the Covariance

1. The covariance of two constants, c and k, is zero.
2. The covariance of two independent random variables is zero.
When X and Y are independent.
3. The covariance is a combinative as is obvious from the definition.
4. The covariance of a random variable with a constant is zero.
5. Adding a constant to either or both random variables does not change their covariances.
6. Multiplying a random variable by a constant multiplies the covariance by that constant.
7. The additive law of covariance holds that the covariance of a random variable with a sum of random variables is just the sum of the covariances with each of the random variables.
8. The covariance of a variable with itself is the variance of the random variable.