The discrete random variable \(X\) takes the values 1, 4, 5, 7, and 9 only. The probability distribution of \(X\) is shown in the table.
| \(x\) | 1 | 4 | 5 | 7 | 9 |
|---|
| \(P(X = x)\) | 4p | 5p^2 | 1.5p | 2.5p | 1.5p |
|---|
Find \(p\).
Solution
The sum of all probabilities must equal 1:
\(4p + 5p^2 + 1.5p + 2.5p + 1.5p = 1\)
Simplify the equation:
\(10p^2 + 19p = 1\)
Rearrange to form a quadratic equation:
\(10p^2 + 19p - 1 = 0\)
Using the quadratic formula \(p = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\), where \(a = 10\), \(b = 19\), and \(c = -1\):
\(p = \frac{-19 \pm \sqrt{19^2 - 4 \times 10 \times (-1)}}{2 \times 10}\)
\(p = \frac{-19 \pm \sqrt{361 + 40}}{20}\)
\(p = \frac{-19 \pm \sqrt{401}}{20}\)
Calculating the roots, we find \(p = 0.1\) or \(p = -2\).
Since probability cannot be negative, \(p = 0.1\).
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