A random variable X has the probability distribution shown in the following table, where p is a constant.
- Find the value of p.
- Given that \(E(X) = 1.15\), find \(\text{Var}(X)\).
Solution
(i) The sum of all probabilities must equal 1:
\(6p + 0.1 = 1\)
Solving for \(p\):
\(6p = 0.9\)
\(p = 0.15\)
(ii) The variance \(\text{Var}(X)\) is calculated using:
\(\text{Var}(X) = (-1)^2 \times p + 0^2 \times p + 1^2 \times 2p + 2^2 \times 2p + 4^2 \times 0.1 - (1.15)^2\)
Substitute \(p = 0.15\):
\(\text{Var}(X) = 1 \times 0.15 + 0 + 1 \times 0.3 + 4 \times 0.3 + 16 \times 0.1 - 1.15^2\)
\(= 0.15 + 0 + 0.3 + 1.2 + 1.6 - 1.3225\)
\(= 1.9275\)
Rounded to three significant figures:
\(\text{Var}(X) = 1.93\)
Log in to record attempts.