Question
A random variable has the following probability distribution:
$X = X_i$ $1$ $2$ $3$ $4$
$P(X = X_i)$ $k$ $2k$ $3k$ $4k$
Write the value of $\text{P}(\text{X}\geq3).$

Answer

Here,
$X = X_i$ $1$ $2$ $3$ $4$
$P(X = X_i)$ $k$ $2k$ $3k$ $4k$
Since, $\sum\text{P}(\text{X})=1$
$\Rightarrow P(X = 1) + P(X = 2) + P(X = 3) + P(X = 4) = 1$
$\Rightarrow k + 2k + 3k + 4k =1$
$\Rightarrow 10k = 1$
$\Rightarrow\text{k}=\frac{1}{10}$
$\text{P}(\text{X}\geq3)= P(X = 3) + P(X = 4)$
$= 3k + 4k$
$= 7k  =\frac{1}{10}$
$\text{P}(\text{X}\geq3)=\frac{7}{10}$

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