A discrete random variable X has the probability distribution given below:
(i) Find the value of k. (ii) Determine the mean of the distribution.
To find the value of k we will be using the very basic idea of probability.
Note: We know that the sum of the probabilities of all random variables taken from a given sample space is equal to 1.
∴ P(X=0.5) + P(X=1) + P(X=1.5) + P(X=2) = 1
∴ k + k2 + 2k2 + k = 1
⇒ 3k2 + 2k – 1 = 0
⇒ 3k2 + 3k - k – 1 = 0
⇒ 3k(k+1) – (k+1) = 0
⇒ (3k-1)(k+1) = 0
∴ k = 1/3 or k = -1
∵ k represents probability of an event. Hence 0≤P(X)≤1
∴ k = 1/3
Mean of any probability distribution is given by- Mean = ∑xipi
Now we have,
X: 0.5 1 1.5 2
P(X): 1/3 1/9 2/9 1/3
∴ first we need to find the product i.e. pixi and add them to get mean.
∴ Mean = 0.5 x (1/3) + 1 x (1/9) + 1.5 x (2/9) +2 x (1/3)