3 A play is enjoying a long run at a theatre. It is found that the play time may be modelled as a normal variable with mean 130 minutes and standard deviation 3 minutes, and that the length of the intermission in the middle of the performance may be modelled by a normal variable with mean 15 minutes and standard deviaton 5 minutes. Find the probability that the performance is completed in less than 140 minutes.

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### Probability Calculation of Play Completion Time

Consider a play that is being performed regularly at a local theatre. The duration of the play and its intermission can both be described using normal distributions.

#### Given Data:
1. **Play Time:**
   - Mean (\(\mu_{\text{play}}\)): 130 minutes
   - Standard Deviation (\(\sigma_{\text{play}}\)): 3 minutes
   
2. **Intermission Time:**
   - Mean (\(\mu_{\text{intermission}}\)): 15 minutes
   - Standard Deviation (\(\sigma_{\text{intermission}}\)): 5 minutes

We aim to find the probability that the total performance (play plus intermission) is completed within 140 minutes.

### Aggregated Distribution of Performance Time

Define:
- \(X\): Random variable representing the play time
- \(Y\): Random variable representing the intermission time

These variables are independently normally distributed:
- \(X \sim N(130, 3^2)\)
- \(Y \sim N(15, 5^2)\)

The total performance time \(Z\) is the sum of \(X\) and \(Y\):
\[ Z = X + Y \]

The mean (\(\mu_Z\)) and variance (\( \sigma_Z^2 \)) of \(Z\) are given by:
\[ \mu_Z = \mu_{\text{play}} + \mu_{\text{intermission}} = 130 + 15 = 145 \]
\[ \sigma_Z^2 = \sigma_{\text{play}}^2 + \sigma_{\text{intermission}}^2 = 3^2 + 5^2 = 9 + 25 = 34 \]
\[ \sigma_Z = \sqrt{34} \]

Thus, \(Z\) follows a normal distribution:
\[ Z \sim N(145, \sqrt{34}) \]

### Probability Calculation

We need to calculate:
\[ P(Z < 140) \]

### Standardizing the Normal Variable

Convert \(Z\) to the standard normal variable \(Z'\):
\[ Z' = \frac{Z - \mu_Z}{\sigma_Z} = \frac{140 - 145}{\sqrt{34}} = \frac{140 - 145}{5.831} = -0.857 \]

### Using the Standard Normal Distribution Table

Determine the probability corresponding to
Transcribed Image Text:### Probability Calculation of Play Completion Time Consider a play that is being performed regularly at a local theatre. The duration of the play and its intermission can both be described using normal distributions. #### Given Data: 1. **Play Time:** - Mean (\(\mu_{\text{play}}\)): 130 minutes - Standard Deviation (\(\sigma_{\text{play}}\)): 3 minutes 2. **Intermission Time:** - Mean (\(\mu_{\text{intermission}}\)): 15 minutes - Standard Deviation (\(\sigma_{\text{intermission}}\)): 5 minutes We aim to find the probability that the total performance (play plus intermission) is completed within 140 minutes. ### Aggregated Distribution of Performance Time Define: - \(X\): Random variable representing the play time - \(Y\): Random variable representing the intermission time These variables are independently normally distributed: - \(X \sim N(130, 3^2)\) - \(Y \sim N(15, 5^2)\) The total performance time \(Z\) is the sum of \(X\) and \(Y\): \[ Z = X + Y \] The mean (\(\mu_Z\)) and variance (\( \sigma_Z^2 \)) of \(Z\) are given by: \[ \mu_Z = \mu_{\text{play}} + \mu_{\text{intermission}} = 130 + 15 = 145 \] \[ \sigma_Z^2 = \sigma_{\text{play}}^2 + \sigma_{\text{intermission}}^2 = 3^2 + 5^2 = 9 + 25 = 34 \] \[ \sigma_Z = \sqrt{34} \] Thus, \(Z\) follows a normal distribution: \[ Z \sim N(145, \sqrt{34}) \] ### Probability Calculation We need to calculate: \[ P(Z < 140) \] ### Standardizing the Normal Variable Convert \(Z\) to the standard normal variable \(Z'\): \[ Z' = \frac{Z - \mu_Z}{\sigma_Z} = \frac{140 - 145}{\sqrt{34}} = \frac{140 - 145}{5.831} = -0.857 \] ### Using the Standard Normal Distribution Table Determine the probability corresponding to
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