Answer:

0.64 = 64% probability that the student passes both subjects.

0.86 = 86% probability that the student passes at least one of the two subjects

Step-by-step explanation:

Conditional Probability

We use the conditional probability formula to solve this question. It is

[tex]P(B|A) = \frac{P(A \cap B)}{P(A)}[/tex]

In which

P(B|A) is the probability of event B happening, given that A happened.

[tex]P(A \cap B)[/tex] is the probability of both A and B happening.

P(A) is the probability of A happening.

In this question:

Event A: Passing subject A

Event B: Passing subject B

The probability of passing subject A is 0.8.

This means that [tex]P(A) = 0.8[/tex]

If you have passed subject A, the probability of passing subject B is 0.8.

This means that [tex]P(B|A) = 0.8[/tex]

Find the probability that the student passes both subjects?

This is [tex]P(A \cap B)[/tex]. So

[tex]P(B|A) = \frac{P(A \cap B)}{P(A)}[/tex]

[tex]P(A \cap B) = P(B|A)P(A) = 0.8*0.8 = 0.64[/tex]

0.64 = 64% probability that the student passes both subjects.

Find the probability that the student passes at least one of the two subjects

This is:

[tex]p = P(A) + P(B) – P(A \cap B)[/tex]

Considering [tex]P(B) = 0.7[/tex], we have that:

[tex]p = P(A) + P(B) – P(A \cap B) = 0.8 + 0.7 – 0.64 = 0.86[/tex]

0.86 = 86% probability that the student passes at least one of the two subjects