Answer:
(1) The value of P (A) is 0.4286.
(2) The value of P (B) is 0.50.
(3) The value of P (A ∩ B) is 0.2143.
(4) The the value of P (B|A) is 0.50.
(5) The events <em>A</em> and <em>B</em> are independent.
Step-by-step explanation:
The events are defined as follows:
<em>A</em> = a student in the class has a sister
<em>B</em> = a student has a brother
The information provided is:
<em>N</em> = 210
n (A) = 90
n (B) = 105
n (A ∩ B) = 45
The probability of an event <em>E</em> is the ratio of the favorable number of outcomes to the total number of outcomes.
![P(E)=\frac{n(E)}{N}](https://tex.z-dn.net/?f=P%28E%29%3D%5Cfrac%7Bn%28E%29%7D%7BN%7D)
The conditional probability of an event <em>X</em> provided that another event <em>Y</em> has already occurred is:
![P(X|Y)=\frac{P(A\cap Y)}{P(Y)}](https://tex.z-dn.net/?f=P%28X%7CY%29%3D%5Cfrac%7BP%28A%5Ccap%20Y%29%7D%7BP%28Y%29%7D)
If the events <em>X</em> and <em>Y</em> are independent then,
![P(X|Y)=P(X)](https://tex.z-dn.net/?f=P%28X%7CY%29%3DP%28X%29)
(1)
Compute the probability of event <em>A</em> as follows:
![P(A)=\frac{n(A)}{N}\\\\=\frac{90}{210}\\\\=0.4286](https://tex.z-dn.net/?f=P%28A%29%3D%5Cfrac%7Bn%28A%29%7D%7BN%7D%5C%5C%5C%5C%3D%5Cfrac%7B90%7D%7B210%7D%5C%5C%5C%5C%3D0.4286)
The value of P (A) is 0.4286.
(2)
Compute the probability of event <em>B</em> as follows:
![P(B)=\frac{n(B)}{N}\\\\=\frac{105}{210}\\\\=0.50](https://tex.z-dn.net/?f=P%28B%29%3D%5Cfrac%7Bn%28B%29%7D%7BN%7D%5C%5C%5C%5C%3D%5Cfrac%7B105%7D%7B210%7D%5C%5C%5C%5C%3D0.50)
The value of P (B) is 0.50.
(3)
Compute the probability of event <em>A</em> and <em>B</em> as follows:
![P(A\cap B)=\frac{n(A\cap B)}{N}\\\\=\frac{45}{210}\\\\=0.2143](https://tex.z-dn.net/?f=P%28A%5Ccap%20B%29%3D%5Cfrac%7Bn%28A%5Ccap%20B%29%7D%7BN%7D%5C%5C%5C%5C%3D%5Cfrac%7B45%7D%7B210%7D%5C%5C%5C%5C%3D0.2143)
The value of P (A ∩ B) is 0.2143.
(4)
Compute the probability of <em>B</em> given <em>A</em> as follows:
![P(B|A)=\frac{P(A\cap B)}{P(A)}\\\\=\frac{0.2143}{0.4286}\\\\=0.50](https://tex.z-dn.net/?f=P%28B%7CA%29%3D%5Cfrac%7BP%28A%5Ccap%20B%29%7D%7BP%28A%29%7D%5C%5C%5C%5C%3D%5Cfrac%7B0.2143%7D%7B0.4286%7D%5C%5C%5C%5C%3D0.50)
The the value of P (B|A) is 0.50.
(5)
The value of P (B|A) = 0.50 = P (B).
Thus, the events <em>A</em> and <em>B</em> are independent.