College

Suppose that [tex] n(U) = 200, n(A) = 105, n(B) = 115 [/tex], and [tex] n(A \cap B) = 30 [/tex].

Find [tex] n \left( A^{c} \cup B \right) [/tex].

A. 115
B. 95
C. 85
D. 75
E. 125
F. None of the above.

Answer :

Let's solve the problem step-by-step using the provided information:

We are given:
- [tex]\( n(U) = 200 \)[/tex]
- [tex]\( n(A) = 105 \)[/tex]
- [tex]\( n(B) = 115 \)[/tex]
- [tex]\( n(A \cap B) = 30 \)[/tex]

We need to find [tex]\( n(A^c \cup B) \)[/tex].

### Step 1: Find [tex]\( n(A \cup B) \)[/tex]

We can use the formula for the union of two sets:

[tex]\[
n(A \cup B) = n(A) + n(B) - n(A \cap B)
\][/tex]

Substitute the given values:

[tex]\[
n(A \cup B) = 105 + 115 - 30 = 190
\][/tex]

### Step 2: Find [tex]\( n(A^c) \)[/tex]

The complement of set [tex]\( A \)[/tex] is all elements in the universal set [tex]\( U \)[/tex] that are not in [tex]\( A \)[/tex]. So,

[tex]\[
n(A^c) = n(U) - n(A)
\][/tex]

Substitute the known values:

[tex]\[
n(A^c) = 200 - 105 = 95
\][/tex]

### Step 3: Find [tex]\( n(A^c \cup B) \)[/tex]

By definition, [tex]\( A^c \cup B \)[/tex] includes all elements that are either not in [tex]\( A \)[/tex] or are in [tex]\( B \)[/tex]. We find this by using the union of the complement of [tex]\( A \)[/tex] with [tex]\( B \)[/tex]:

From the previous steps, we have already found that:

- [tex]\( n(A^c) = 95 \)[/tex]
- [tex]\( n(A \cup B) = 190 \)[/tex]

Now, using these, the total number of elements in [tex]\( A^c \cup B \)[/tex] is equal to the total number of elements in the universal set, [tex]\( n(U) \)[/tex], since [tex]\( A^c \cup B \)[/tex] encompasses all elements in [tex]\( U \)[/tex].

[tex]\[
n(A^c \cup B) = 200
\][/tex]

Thus, the correct answer is [tex]\( 200 \)[/tex], which is not listed among the options. Therefore, the correct answer is None of the above.