Q72 / 150 · MHT CET 2025 (22 Apr Shift 1) · Mathematics

The p.d.f. of a continuous random variable X is $\mathrm{f}(x)=\left\{\begin{array}{cc} \frac{x^2}{18} & \text { if }-3 < x < 3 \\ 0 & \text { otherwise } \end{array}\right.$ Then $\mathrm{P}[|\mathrm{X}| < 2]=$

  • A
    $\frac{1}{27}$
  • B
    $\frac{2}{13}$
  • Correct answer
    C
    $\frac{8}{27}$
  • D
    $\frac{4}{27}$

Solution

The probability density function is defined by $\mathrm{f}(x) = \begin{cases} \frac{x^2}{18} & \text{if } -3 < x < 3 \\ 0 & \text{otherwise} \end{cases}$.

Since $|X| < 2$ implies $-2 < X < 2$ and this interval lies within $(-3, 3)$, the probability is

$\mathrm{P}[|X| < 2] = \int_{-2}^{2} \frac{x^2}{18} \, dx$.

Integrating yields

$\frac{1}{18} \left[ \frac{x^3}{3} \right]_{-2}^{2} = \frac{1}{18} \left( \frac{8}{3} - \frac{-8}{3} \right) = \frac{1}{18} \cdot \frac{16}{3} = \frac{16}{54} = \frac{8}{27}$.

This corresponds to option C.

Hence, the correct answer is option: 'C'.

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