Anonymous asked in Science & MathematicsMathematics · 8 years ago

Calculate the expected value and variance of the random variable?

Calculate the expected value and variance of the random variable Y=10X + 5.

The probability distribution for random variable X is

x P(X=x)

2 0.07

5 0.23

8 0.34

11 0.36

Here is what i have worked out so far.

Forcast amount


variance of x

2^2(0.07)+5^2(0.23)+8^5(0.34)+11^2(0.36)= 71.35

Var(x)= 71.35-7.97^2 = 7.83

Any help would be much appreciated.


perfect, i had the same answer for the expected value! but am not quite sure how you have done the variance?

2 Answers

  • 8 years ago
    Favorite Answer

    mml -

    Your formulas are perfect! I'm going to assume your math is correct ...

    E(Y) = E(10X + 5) = 10(7.97) + 5 = 84.7

    V(Y) = V(10X + 5) = 10^2 V(X) = 100(7.83) = 783

    So, always ignore a constant term that is added or subtracted for the variance. BUT, a constant times a variance is always the constant squared.

    Hope that helps

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  • larry
    Lv 4
    3 years ago

    there's a smart formula to get the variance V[x] = E[x^2] - E[x]^2 in words: variance of x is comparable to the envisioned fee of x minus the advise squared. having discovered the advise, you need to in common terms discover envisioned fee of x^2 and replace into the formula, you're able to do this the comparable way you discovered E[x] yet this time replace x with x^2. sturdy luck. :)

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