Skip to main contentSkip to solution

The probability distribution of the random variable X is given by

X0123
P(X)0.2k2k2k

The variance of the random variable X is

Solution

✅ Correct Option: 1

The sum of all probabilities in a probability distribution must equal 1.

P(X=0)+P(X=1)+P(X=2)+P(X=3)=1P(X=0) + P(X=1) + P(X=2) + P(X=3) = 1

0.2+k+2k+2k=10.2 + k + 2k + 2k = 1

0.2+5k=10.2 + 5k = 1

5k=0.85k = 0.8

k=0.16=425k = 0.16 = \frac{4}{25}


The complete probability distribution is:

X0123
P(X)15\frac{1}{5}425\frac{4}{25}825\frac{8}{25}825\frac{8}{25}

The mean is given by E(X)=∑x⋅P(x)E(X) = \sum x \cdot P(x)

E(X)=0×525+1×425+2×825+3×825E(X) = 0 \times \frac{5}{25} + 1 \times \frac{4}{25} + 2 \times \frac{8}{25} + 3 \times \frac{8}{25}

=0+425+1625+2425= 0 + \frac{4}{25} + \frac{16}{25} + \frac{24}{25}

=4425= \frac{44}{25}


E(X2)=∑x2⋅P(x)E(X^2) = \sum x^2 \cdot P(x)

E(X2)=02×525+12×425+22×825+32×825E(X^2) = 0^2 \times \frac{5}{25} + 1^2 \times \frac{4}{25} + 2^2 \times \frac{8}{25} + 3^2 \times \frac{8}{25}

=0+425+4×825+9×825= 0 + \frac{4}{25} + 4 \times \frac{8}{25} + 9 \times \frac{8}{25}

=425+3225+7225= \frac{4}{25} + \frac{32}{25} + \frac{72}{25}

=10825= \frac{108}{25}


The variance is given by Var(X)=E(X2)−[E(X)]2\text{Var}(X) = E(X^2) - [E(X)]^2

Var(X)=10825−(4425)2\text{Var}(X) = \frac{108}{25} - \left(\frac{44}{25}\right)^2

=10825−1936625= \frac{108}{25} - \frac{1936}{625}

=2700625−1936625= \frac{2700}{625} - \frac{1936}{625}

=764625= \frac{764}{625}

Therefore, the variance of the random variable X is 764625\frac{764}{625}.

Keyboard Shortcuts

  • Left arrow: Previous question
  • Right arrow: Next question
  • S key: Jump to solution
  • Q key: Jump to question