The sum of all probabilities in a probability distribution must equal 1.
P(X=0)+P(X=1)+P(X=2)+P(X=3)=1
0.2+k+2k+2k=1
0.2+5k=1
5k=0.8
k=0.16=254
The complete probability distribution is:
| X | 0 | 1 | 2 | 3 |
|---|
| P(X) | 51 | 254 | 258 | 258 |
The mean is given by E(X)=∑x⋅P(x)
E(X)=0×255+1×254+2×258+3×258
=0+254+2516+2524
=2544
E(X2)=∑x2⋅P(x)
E(X2)=02×255+12×254+22×258+32×258
=0+254+4×258+9×258
=254+2532+2572
=25108
The variance is given by Var(X)=E(X2)−[E(X)]2
Var(X)=25108−(2544)2
=25108−6251936
=6252700−6251936
=625764
Therefore, the variance of the random variable X is 625764.