Suppose X and Y are independent random variables and that X~ on (2,5). Calculate the probability that 2X + Y < 8. Exp(14) and Y is uniformly distributed Proposed solution: Because X and Y are independent, the joint p.d.f. is given by the product of the p.d.f. of X and of Y,

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**Problem Statement:**

Suppose \( X \) and \( Y \) are independent random variables and that \( X \sim \text{Exp}(14) \) and \( Y \) is uniformly distributed on (2, 5). Calculate the probability that \( 2X + Y < 8 \).

**Proposed Solution:**

Because \( X \) and \( Y \) are independent, the joint probability density function (p.d.f.) is given by the product of the p.d.f. of \( X \) and \( Y \), that is

\[
f_{X,Y}(x, y) = 
\begin{cases} 
\frac{1}{3} e^{-14x} & \text{if } x > 0, y > 0 \\
0 & \text{otherwise.}
\end{cases}
\]

**Solution Details:**

The desired probability is calculated as follows:

\[
\mathbb{P}(2X + Y < 8) = \int_{4}^{10} \int_{0}^{8-y} \frac{1}{3} e^{-14s} \, ds \, dt = \int_{4}^{10} \left[ -\frac{1}{42} e^{-14s} \right]_{0}^{8-t} \, dt
\]

This simplifies to:

\[
= \int_{4}^{10} \frac{14}{3} \left( 1 - e^{-14(8-t)} \right) dt = \frac{14}{3} \left[ t - \frac{1}{14} e^{-14(8-t)} \right]_{4}^{10}
\]

Evaluating this expression results in:

\[
= 28 - \frac{1}{14} (e^{-56} - e^{-28}).
\]

This provides the solution to the probability problem using integration of the joint probability density function over the specified limits.
Transcribed Image Text:**Problem Statement:** Suppose \( X \) and \( Y \) are independent random variables and that \( X \sim \text{Exp}(14) \) and \( Y \) is uniformly distributed on (2, 5). Calculate the probability that \( 2X + Y < 8 \). **Proposed Solution:** Because \( X \) and \( Y \) are independent, the joint probability density function (p.d.f.) is given by the product of the p.d.f. of \( X \) and \( Y \), that is \[ f_{X,Y}(x, y) = \begin{cases} \frac{1}{3} e^{-14x} & \text{if } x > 0, y > 0 \\ 0 & \text{otherwise.} \end{cases} \] **Solution Details:** The desired probability is calculated as follows: \[ \mathbb{P}(2X + Y < 8) = \int_{4}^{10} \int_{0}^{8-y} \frac{1}{3} e^{-14s} \, ds \, dt = \int_{4}^{10} \left[ -\frac{1}{42} e^{-14s} \right]_{0}^{8-t} \, dt \] This simplifies to: \[ = \int_{4}^{10} \frac{14}{3} \left( 1 - e^{-14(8-t)} \right) dt = \frac{14}{3} \left[ t - \frac{1}{14} e^{-14(8-t)} \right]_{4}^{10} \] Evaluating this expression results in: \[ = 28 - \frac{1}{14} (e^{-56} - e^{-28}). \] This provides the solution to the probability problem using integration of the joint probability density function over the specified limits.
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