Answer:
(a) Name: Multinomial distribution
Parameters:
![n = 20](https://tex.z-dn.net/?f=n%20%3D%2020)
(b) Range: ![\{(x,y,z)| x + y + z=20\}](https://tex.z-dn.net/?f=%5C%7B%28x%2Cy%2Cz%29%7C%20x%20%2B%20y%20%2B%20z%3D20%5C%7D)
(c) Name: Binomial distribution
Parameters:
![n = 20](https://tex.z-dn.net/?f=n%20%3D%2020)
![Var(x) = 0.95](https://tex.z-dn.net/?f=Var%28x%29%20%3D%200.95)
![(e)\ P(X = 1, Y = 17, Z = 3) = 0](https://tex.z-dn.net/?f=%28e%29%5C%20P%28X%20%3D%201%2C%20Y%20%3D%2017%2C%20Z%20%3D%203%29%20%3D%200)
![(f)\ P(X \le 1, Y = 17, Z = 3) =0.07195](https://tex.z-dn.net/?f=%28f%29%5C%20P%28X%20%5Cle%201%2C%20Y%20%3D%2017%2C%20Z%20%3D%203%29%20%3D0.07195)
![(g)\ P(X \le 1) = 0.7359](https://tex.z-dn.net/?f=%28g%29%5C%20P%28X%20%5Cle%201%29%20%3D%200.7359)
![(h)\ E(Y) = 17](https://tex.z-dn.net/?f=%28h%29%5C%20E%28Y%29%20%3D%2017)
Step-by-step explanation:
Given
![p_1 = 5\%](https://tex.z-dn.net/?f=p_1%20%3D%205%5C%25)
![p_2 = 85\%](https://tex.z-dn.net/?f=p_2%20%3D%2085%5C%25)
![p_3 = 10\%](https://tex.z-dn.net/?f=p_3%20%3D%2010%5C%25)
![n = 20](https://tex.z-dn.net/?f=n%20%3D%2020)
High Slabs
Medium Slabs
Low Slabs
Solving (a): Names and values of joint pdf of X, Y and Z
Given that:
Number of voids considered as high slabs
Number of voids considered as medium slabs
Number of voids considered as low slabs
Since the variables are more than 2 (2 means binomial), then the name is multinomial distribution
The parameters are:
![n = 20](https://tex.z-dn.net/?f=n%20%3D%2020)
And the mass function is:
![f_{XYZ} = P(X = x; Y = y; Z = z) = \frac{n!}{x!y!z!} * p_1^xp_2^yp_3^z](https://tex.z-dn.net/?f=f_%7BXYZ%7D%20%3D%20P%28X%20%3D%20x%3B%20Y%20%3D%20y%3B%20Z%20%3D%20z%29%20%3D%20%5Cfrac%7Bn%21%7D%7Bx%21y%21z%21%7D%20%2A%20p_1%5Exp_2%5Eyp_3%5Ez)
Solving (b): The range of the joint pdf of X, Y and Z
Given that:
![n = 20](https://tex.z-dn.net/?f=n%20%3D%2020)
The number of voids (x, y and z) cannot be negative and they must be integers; So:
![x + y + z = n](https://tex.z-dn.net/?f=x%20%2B%20y%20%2B%20z%20%3D%20n)
![x + y + z = 20](https://tex.z-dn.net/?f=x%20%2B%20y%20%2B%20z%20%3D%2020)
Hence, the range is:
![\{(x,y,z)| x + y + z=20\}](https://tex.z-dn.net/?f=%5C%7B%28x%2Cy%2Cz%29%7C%20x%20%2B%20y%20%2B%20z%3D20%5C%7D)
Solving (c): Names and values of marginal pdf of X
We have the following parameters attributed to X:
and ![n = 20](https://tex.z-dn.net/?f=n%20%3D%2020)
Hence, the name is: Binomial distribution
Solving (d): E(x) and Var(x)
In (c), we have:
and ![n = 20](https://tex.z-dn.net/?f=n%20%3D%2020)
![E(x) = p_1* n](https://tex.z-dn.net/?f=E%28x%29%20%3D%20p_1%2A%20n)
![E(x) = 5\% * 20](https://tex.z-dn.net/?f=E%28x%29%20%3D%205%5C%25%20%2A%2020)
![E(x) = 1](https://tex.z-dn.net/?f=E%28x%29%20%3D%201)
![Var(x) = E(x) * (1 - p_1)](https://tex.z-dn.net/?f=Var%28x%29%20%3D%20E%28x%29%20%2A%20%281%20-%20p_1%29)
![Var(x) = 1 * (1 - 5\%)](https://tex.z-dn.net/?f=Var%28x%29%20%3D%201%20%2A%20%281%20-%205%5C%25%29)
![Var(x) = 1 * 0.95](https://tex.z-dn.net/?f=Var%28x%29%20%3D%201%20%2A%200.95)
![Var(x) = 0.95](https://tex.z-dn.net/?f=Var%28x%29%20%3D%200.95)
![(e)\ P(X = 1, Y = 17, Z = 3)](https://tex.z-dn.net/?f=%28e%29%5C%20P%28X%20%3D%201%2C%20Y%20%3D%2017%2C%20Z%20%3D%203%29)
In (b), we have: ![x + y + z = 20](https://tex.z-dn.net/?f=x%20%2B%20y%20%2B%20z%20%3D%2020)
However, the given values of x in this question implies that:
![x + y + z = 1 + 17 + 3](https://tex.z-dn.net/?f=x%20%2B%20y%20%2B%20z%20%3D%201%20%2B%2017%20%2B%203)
![x + y + z = 21](https://tex.z-dn.net/?f=x%20%2B%20y%20%2B%20z%20%3D%2021)
Hence:
![P(X = 1, Y = 17, Z = 3) = 0](https://tex.z-dn.net/?f=P%28X%20%3D%201%2C%20Y%20%3D%2017%2C%20Z%20%3D%203%29%20%3D%200)
![(f)\ P{X \le 1, Y = 17, Z = 3)](https://tex.z-dn.net/?f=%28f%29%5C%20P%7BX%20%5Cle%201%2C%20Y%20%3D%2017%2C%20Z%20%3D%203%29)
This question implies that:
![P(X \le 1, Y = 17, Z = 3) =P(X = 0, Y = 17, Z = 3) + P(X = 1, Y = 17, Z = 3)](https://tex.z-dn.net/?f=P%28X%20%5Cle%201%2C%20Y%20%3D%2017%2C%20Z%20%3D%203%29%20%3DP%28X%20%3D%200%2C%20Y%20%3D%2017%2C%20Z%20%3D%203%29%20%2B%20P%28X%20%3D%201%2C%20Y%20%3D%2017%2C%20Z%20%3D%203%29)
Because
--- for x
In (e), we have:
![P(X = 1, Y = 17, Z = 3) = 0](https://tex.z-dn.net/?f=P%28X%20%3D%201%2C%20Y%20%3D%2017%2C%20Z%20%3D%203%29%20%3D%200)
So:
![P(X \le 1, Y = 17, Z = 3) =P(X = 0, Y = 17, Z = 3) +0](https://tex.z-dn.net/?f=P%28X%20%5Cle%201%2C%20Y%20%3D%2017%2C%20Z%20%3D%203%29%20%3DP%28X%20%3D%200%2C%20Y%20%3D%2017%2C%20Z%20%3D%203%29%20%2B0)
![P(X \le 1, Y = 17, Z = 3) =P(X = 0, Y = 17, Z = 3)](https://tex.z-dn.net/?f=P%28X%20%5Cle%201%2C%20Y%20%3D%2017%2C%20Z%20%3D%203%29%20%3DP%28X%20%3D%200%2C%20Y%20%3D%2017%2C%20Z%20%3D%203%29)
In (a), we have:
![f_{XYZ} = P(X = x; Y = y; Z = z) = \frac{n!}{x!y!z!} * p_1^xp_2^yp_3^z](https://tex.z-dn.net/?f=f_%7BXYZ%7D%20%3D%20P%28X%20%3D%20x%3B%20Y%20%3D%20y%3B%20Z%20%3D%20z%29%20%3D%20%5Cfrac%7Bn%21%7D%7Bx%21y%21z%21%7D%20%2A%20p_1%5Exp_2%5Eyp_3%5Ez)
So:
![P(X=0; Y=17; Z = 3) = \frac{20!}{0! * 17! * 3!} * (5\%)^0 * (85\%)^{17} * (10\%)^{3}](https://tex.z-dn.net/?f=P%28X%3D0%3B%20Y%3D17%3B%20Z%20%3D%203%29%20%3D%20%5Cfrac%7B20%21%7D%7B0%21%20%2A%2017%21%20%2A%203%21%7D%20%2A%20%285%5C%25%29%5E0%20%2A%20%2885%5C%25%29%5E%7B17%7D%20%2A%20%2810%5C%25%29%5E%7B3%7D)
![P(X=0; Y=17; Z = 3) = \frac{20!}{1 * 17! * 3!} * 1 * (85\%)^{17} * (10\%)^{3}](https://tex.z-dn.net/?f=P%28X%3D0%3B%20Y%3D17%3B%20Z%20%3D%203%29%20%3D%20%5Cfrac%7B20%21%7D%7B1%20%2A%2017%21%20%2A%203%21%7D%20%2A%201%20%2A%20%2885%5C%25%29%5E%7B17%7D%20%2A%20%2810%5C%25%29%5E%7B3%7D)
![P(X=0; Y=17; Z = 3) = \frac{20!}{17! * 3!} * (85\%)^{17} * (10\%)^{3}](https://tex.z-dn.net/?f=P%28X%3D0%3B%20Y%3D17%3B%20Z%20%3D%203%29%20%3D%20%5Cfrac%7B20%21%7D%7B17%21%20%2A%203%21%7D%20%2A%20%2885%5C%25%29%5E%7B17%7D%20%2A%20%2810%5C%25%29%5E%7B3%7D)
Expand
![P(X=0; Y=17; Z = 3) = \frac{20*19*18*17!}{17! * 3*2*1} * (85\%)^{17} * (10\%)^{3}](https://tex.z-dn.net/?f=P%28X%3D0%3B%20Y%3D17%3B%20Z%20%3D%203%29%20%3D%20%5Cfrac%7B20%2A19%2A18%2A17%21%7D%7B17%21%20%2A%203%2A2%2A1%7D%20%2A%20%2885%5C%25%29%5E%7B17%7D%20%2A%20%2810%5C%25%29%5E%7B3%7D)
![P(X=0; Y=17; Z = 3) = \frac{20*19*18}{6} * (85\%)^{17} * (10\%)^{3}](https://tex.z-dn.net/?f=P%28X%3D0%3B%20Y%3D17%3B%20Z%20%3D%203%29%20%3D%20%5Cfrac%7B20%2A19%2A18%7D%7B6%7D%20%2A%20%2885%5C%25%29%5E%7B17%7D%20%2A%20%2810%5C%25%29%5E%7B3%7D)
![P(X=0; Y=17; Z = 3) = 20*19*3 * (85\%)^{17} * (10\%)^{3}](https://tex.z-dn.net/?f=P%28X%3D0%3B%20Y%3D17%3B%20Z%20%3D%203%29%20%3D%2020%2A19%2A3%20%2A%20%2885%5C%25%29%5E%7B17%7D%20%2A%20%2810%5C%25%29%5E%7B3%7D)
Using a calculator, we have:
![P(X=0; Y=17; Z = 3) = 0.07195](https://tex.z-dn.net/?f=P%28X%3D0%3B%20Y%3D17%3B%20Z%20%3D%203%29%20%3D%200.07195)
So:
![P(X \le 1, Y = 17, Z = 3) =P(X = 0, Y = 17, Z = 3)](https://tex.z-dn.net/?f=P%28X%20%5Cle%201%2C%20Y%20%3D%2017%2C%20Z%20%3D%203%29%20%3DP%28X%20%3D%200%2C%20Y%20%3D%2017%2C%20Z%20%3D%203%29)
![P(X \le 1, Y = 17, Z = 3) =0.07195](https://tex.z-dn.net/?f=P%28X%20%5Cle%201%2C%20Y%20%3D%2017%2C%20Z%20%3D%203%29%20%3D0.07195)
![(g)\ P(X \le 1)](https://tex.z-dn.net/?f=%28g%29%5C%20P%28X%20%5Cle%201%29)
This implies that:
![P(X \le 1) = P(X = 0) + P(X = 1)](https://tex.z-dn.net/?f=P%28X%20%5Cle%201%29%20%3D%20P%28X%20%3D%200%29%20%2B%20P%28X%20%3D%201%29)
In (c), we established that X is a binomial distribution with the following parameters:
![n = 20](https://tex.z-dn.net/?f=n%20%3D%2020)
Such that:
![P(X=x) = ^nC_x * p_1^x * (1 - p_1)^{n - x}](https://tex.z-dn.net/?f=P%28X%3Dx%29%20%3D%20%5EnC_x%20%2A%20p_1%5Ex%20%2A%20%281%20-%20p_1%29%5E%7Bn%20-%20x%7D)
So:
![P(X=0) = ^{20}C_0 * (5\%)^0 * (1 - 5\%)^{20 - 0}](https://tex.z-dn.net/?f=P%28X%3D0%29%20%3D%20%5E%7B20%7DC_0%20%2A%20%285%5C%25%29%5E0%20%2A%20%281%20-%205%5C%25%29%5E%7B20%20-%200%7D)
![P(X=0) = ^{20}C_0 * 1 * (1 - 5\%)^{20}](https://tex.z-dn.net/?f=P%28X%3D0%29%20%3D%20%5E%7B20%7DC_0%20%2A%201%20%2A%20%281%20-%205%5C%25%29%5E%7B20%7D)
![P(X=0) = 1 * 1 * (95\%)^{20}](https://tex.z-dn.net/?f=P%28X%3D0%29%20%3D%201%20%2A%201%20%2A%20%2895%5C%25%29%5E%7B20%7D)
![P(X=0) = 0.3585](https://tex.z-dn.net/?f=P%28X%3D0%29%20%3D%200.3585)
![P(X=1) = ^{20}C_1 * (5\%)^1 * (1 - 5\%)^{20 - 1}](https://tex.z-dn.net/?f=P%28X%3D1%29%20%3D%20%5E%7B20%7DC_1%20%2A%20%285%5C%25%29%5E1%20%2A%20%281%20-%205%5C%25%29%5E%7B20%20-%201%7D)
![P(X=1) = 20 * (5\%)* (1 - 5\%)^{19}](https://tex.z-dn.net/?f=P%28X%3D1%29%20%3D%2020%20%2A%20%285%5C%25%29%2A%20%281%20-%205%5C%25%29%5E%7B19%7D)
![P(X=1) = 0.3774](https://tex.z-dn.net/?f=P%28X%3D1%29%20%3D%200.3774)
So:
![P(X \le 1) = P(X = 0) + P(X = 1)](https://tex.z-dn.net/?f=P%28X%20%5Cle%201%29%20%3D%20P%28X%20%3D%200%29%20%2B%20P%28X%20%3D%201%29)
![P(X \le 1) = 0.3585 + 0.3774](https://tex.z-dn.net/?f=P%28X%20%5Cle%201%29%20%3D%200.3585%20%2B%200.3774)
![P(X \le 1) = 0.7359](https://tex.z-dn.net/?f=P%28X%20%5Cle%201%29%20%3D%200.7359)
![(h)\ E(Y)](https://tex.z-dn.net/?f=%28h%29%5C%20E%28Y%29)
Y has the following parameters
and ![n = 20](https://tex.z-dn.net/?f=n%20%3D%2020)
![E(Y) = p_2 * n](https://tex.z-dn.net/?f=E%28Y%29%20%3D%20p_2%20%2A%20n)
![E(Y) = 85\% * 20](https://tex.z-dn.net/?f=E%28Y%29%20%3D%2085%5C%25%20%2A%2020)