The probability distribution of the random variable \(X\) is shown in the following table.
| \(x\) | -2 | -1 | 0 | 1 | 2 | 3 |
|---|
| \(P(X = x)\) | 0.08 | \(p\) | 0.12 | 0.16 | \(q\) | 0.22 |
The mean of \(X\) is 1.05.
- Write down two equations involving \(p\) and \(q\) and hence find the values of \(p\) and \(q\).
- Find the variance of \(X\).
Solution
To find the values of \(p\) and \(q\), we use the following equations:
1. The sum of probabilities: \(0.08 + p + 0.12 + 0.16 + q + 0.22 = 1\)
2. The mean equation: \(-2(0.08) - 1(p) + 0(0.12) + 1(0.16) + 2(q) + 3(0.22) = 1.05\)
Simplifying these equations:
\(p + q = 0.42\)
\(-0.16 - p + 0.16 + 2q + 0.66 = 1.05\)
\(-p + 2q = 0.39\)
Solving these equations simultaneously:
\(p = 0.15\)
\(q = 0.27\)
To find the variance of \(X\), we use the formula:
\(\text{Var}(X) = \sum x^2 P(X = x) - (\text{mean})^2\)
\(\text{Var}(X) = 4(0.08) + p + 0.16 + 4q + 1.98 - (1.05)^2\)
Substituting \(p = 0.15\) and \(q = 0.27\):
\(\text{Var}(X) = 2.59\)
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