Answer:
(a) The mean and standard deviation of <em>X</em> is 2.6 and 1.2 respectively.
(b) The mean and standard deviation of <em>T</em> are 390 and 180 respectively.
(c) The distribution of <em>T</em> is <em>N</em> (390, 180²). The probability that all students’ requests can be accommodated is 0.7291.
Step-by-step explanation:
(a)
The random variable <em>X</em> is defined as the number of tickets requested by a randomly selected graduating student.
The probability distribution of the number of tickets wanted by the students for the graduation ceremony is as follows:
X P (X)
0 0.05
1 0.15
2 0.25
3 0.25
4 0.30
The formula to compute the mean is:
![\mu=\sum x\cdot P(X)](https://tex.z-dn.net/?f=%5Cmu%3D%5Csum%20x%5Ccdot%20P%28X%29)
Compute the mean number of tickets requested by a student as follows:
![\mu=\sum x\cdot P(X)\\=(0\times 0.05)+(1\times 0.15)+(2\times 0.25)+(3\times 0.25)+(4\times 0.30)\\=2.6](https://tex.z-dn.net/?f=%5Cmu%3D%5Csum%20x%5Ccdot%20P%28X%29%5C%5C%3D%280%5Ctimes%200.05%29%2B%281%5Ctimes%200.15%29%2B%282%5Ctimes%200.25%29%2B%283%5Ctimes%200.25%29%2B%284%5Ctimes%200.30%29%5C%5C%3D2.6)
The formula of standard deviation of the number of tickets requested by a student as follows:
![\sigma=\sqrt{E(X^{2})-\mu^{2}}](https://tex.z-dn.net/?f=%5Csigma%3D%5Csqrt%7BE%28X%5E%7B2%7D%29-%5Cmu%5E%7B2%7D%7D)
Compute the standard deviation as follows:
![\sigma=\sqrt{E(X^{2})-\mu^{2}}\\=\sqrt{[(0^{2}\times 0.05)+(1^{2}\times 0.15)+(2^{2}\times 0.25)+(3^{2}\times 0.25)+(4^{2}\times 0.30)]-(2.6)^{2}}\\=\sqrt{1.44}\\=1.2](https://tex.z-dn.net/?f=%5Csigma%3D%5Csqrt%7BE%28X%5E%7B2%7D%29-%5Cmu%5E%7B2%7D%7D%5C%5C%3D%5Csqrt%7B%5B%280%5E%7B2%7D%5Ctimes%200.05%29%2B%281%5E%7B2%7D%5Ctimes%200.15%29%2B%282%5E%7B2%7D%5Ctimes%200.25%29%2B%283%5E%7B2%7D%5Ctimes%200.25%29%2B%284%5E%7B2%7D%5Ctimes%200.30%29%5D-%282.6%29%5E%7B2%7D%7D%5C%5C%3D%5Csqrt%7B1.44%7D%5C%5C%3D1.2)
Thus, the mean and standard deviation of <em>X</em> is 2.6 and 1.2 respectively.
(b)
The random variable <em>T</em> is defined as the total number of tickets requested by the 150 students graduating this year.
That is, <em>T</em> = 150 <em>X</em>
Compute the mean of <em>T</em> as follows:
![\mu=E(T)\\=E(150\cdot X)\\=150\times E(X)\\=150\times 2.6\\=390](https://tex.z-dn.net/?f=%5Cmu%3DE%28T%29%5C%5C%3DE%28150%5Ccdot%20X%29%5C%5C%3D150%5Ctimes%20E%28X%29%5C%5C%3D150%5Ctimes%202.6%5C%5C%3D390)
Compute the standard deviation of <em>T</em> as follows:
![\sigma=SD(T)\\=SD(150\cdot X)\\=\sqrt{V(150\cdot X)}\\=\sqrt{150^{2}}\times SD(X)\\=150\times 1.2\\=180](https://tex.z-dn.net/?f=%5Csigma%3DSD%28T%29%5C%5C%3DSD%28150%5Ccdot%20X%29%5C%5C%3D%5Csqrt%7BV%28150%5Ccdot%20X%29%7D%5C%5C%3D%5Csqrt%7B150%5E%7B2%7D%7D%5Ctimes%20SD%28X%29%5C%5C%3D150%5Ctimes%201.2%5C%5C%3D180)
Thus, the mean and standard deviation of <em>T</em> are 390 and 180 respectively.
(c)
The maximum number of seats at the gym is, 500.
According to the Central Limit Theorem if we have a population with mean μ and standard deviation σ and we take appropriately huge random samples (n ≥ 30) from the population with replacement, then the distribution of the sum of values of X, i.e ∑X, will be approximately normally distributed.
Here <em>T</em> = total number of seats requested.
Then, the mean of the distribution of the sum of values of X is given by,
And the standard deviation of the distribution of the sum of values of X is given by,
![\sigma_{T}=n\times \sigma_{X}=180](https://tex.z-dn.net/?f=%5Csigma_%7BT%7D%3Dn%5Ctimes%20%5Csigma_%7BX%7D%3D180)
So, the distribution of <em>T</em> is N (390, 180²).
Compute the probability that all students’ requests can be accommodated, i.e. less than 500 seats were requested as follows:
![P(T](https://tex.z-dn.net/?f=P%28T%3C500%29%3DP%28%5Cfrac%7BT-%5Cmu_%7BT%7D%7D%7B%5Csigma_%7BT%7D%7D%3C%5Cfrac%7B500-390%7D%7B180%7D%29%5C%5C%3DP%28Z%3C0.61%29%5C%5C%3D0.72907%5C%5C%5Capprox%200.7291)
Thus, the probability that all students’ requests can be accommodated is 0.7291.