At the Rolling Ridge School spelling bee, 75% of the
contestants advanced to the second round and 60% advanced
to the third round. What is the probability that a randomly
selected contestant advanced to the third round given the same
contestant advanced to the second round?
A. 3/20
B. 9/20
c. 7/15
D. 4/5

Respuesta :

Answer: Option D

[tex]P (B | A) =\frac{4}{5}[/tex]

Step-by-step explanation:

Call A to the event in which a student advances to the second round.

We know that:

[tex]P (A) = 75\% = 0.75[/tex]

Call B the event in which a student advances to the third round.

We know that:

[tex]P (B) = 60\% = 0.6[/tex]

We then look for the probability of B given A. This is:

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

In this case, the probability of B and A is equal to the probability of B, since the students who advance to the third round also advanced to the second round before

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

[tex]P (B | A) =\frac{0.6}{0.75}[/tex]

[tex]P (B | A) =\frac{4}{5}[/tex]