If the probability of an event is [tex]\frac{2}{7}[/tex], what must be the probability of its complement?

A. [tex]\frac{1}{7}[/tex]
B. [tex]\frac{2}{7}[/tex]
C. [tex]\frac{4}{7}[/tex]
D. [tex]\frac{5}{7}[/tex]



Answer :

To solve for the probability of the complement of an event, we need to understand a fundamental principle of probability: the sum of the probability of an event and the probability of its complement always equals 1. This is represented mathematically as:

[tex]\[ P(\text{event}) + P(\text{complement}) = 1 \][/tex]

Given that the probability of the event (let's denote it as [tex]\( P(\text{event}) \)[/tex]) is [tex]\(\frac{2}{7}\)[/tex], we want to find the probability of the complement of this event (denoted as [tex]\( P(\text{complement}) \)[/tex]).

Using the principle mentioned above, we can write:

[tex]\[ P(\text{event}) + P(\text{complement}) = 1 \][/tex]

Substituting [tex]\( P(\text{event}) = \frac{2}{7} \)[/tex] into the equation:

[tex]\[ \frac{2}{7} + P(\text{complement}) = 1 \][/tex]

To solve for [tex]\( P(\text{complement}) \)[/tex], we isolate it on one side of the equation by subtracting [tex]\(\frac{2}{7}\)[/tex] from both sides:

[tex]\[ P(\text{complement}) = 1 - \frac{2}{7} \][/tex]

Next, we need to perform the subtraction. To subtract [tex]\(\frac{2}{7}\)[/tex] from 1, we first express 1 as a fraction with a denominator of 7:

[tex]\[ 1 = \frac{7}{7} \][/tex]

Thus, the subtraction becomes:

[tex]\[ P(\text{complement}) = \frac{7}{7} - \frac{2}{7} \][/tex]

Since the denominators are the same, we simply subtract the numerators:

[tex]\[ P(\text{complement}) = \frac{7 - 2}{7} = \frac{5}{7} \][/tex]

So, the probability of the complement of the event is:

[tex]\[ \boxed{\frac{5}{7}} \][/tex]

Therefore, among the given choices, the correct answer is [tex]\(\frac{5}{7}\)[/tex].