1. The distribution table {Pi} of discrete random variable x should have two basic properties: Pi >；; 0 ∑Pi= 1 .

2. The density function fx(x) of continuous random variable X should have two basic properties.

f(x)>0，∫f(x)dx= 1 .

3. let x ~ b (100; 0.2), then E(X) =20 and D(X)= 16.

4. let X~P(2), then E(X) = 2 and D(X)= 2.

5. let x ~ u (2,6), then E(X) =4. D(X)= 4/3 .

6 let X~E(2), then E(X) = 1/2 and D(X)= 1/4.

7. Let E(X) = 5 and D (x) = 1, then E(X squared +2X-6)=30.

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7.A

8.C

9，B

10, which should be -34. The original answer seems to be wrong.