Question

The probability that Janice will attend math class today is 62%. The probability that Ellie will attend math class if Janice attends is 100%. Ellie will not attend the class unless she hears from Janice first. What is the probability that both will attend the class?
73%
100%
81%
62%

Answer 1

Conditional probability: \[
\Pr(A|B)=\frac{\Pr(A\cap B)}{\Pr(B)}
\]

Answer 2

Which means that: \[
\Pr(A\cap B) = \Pr(A|B)\Pr(B)
\]

Answer 3

This makes no scene @wio

Answer 4

You are not familiar with conditional probability?

Answer 5

No

Answer 6

One event is that Janice attends. The other event is that Ellie attends.

Answer 7

A condition event would be that Ellie attends if Janice attends.

Answer 8

So...?

Answer 9

So I think you might want to read your textbook a bit, since you're completely clueless.

Answer 10

I do online school so i dont have a text book with me. Im doing a post test

Answer 11

Here are the possibilities:
Janice attends and Ellie attends
Janice attends and Ellie skips
Janice skips and Ellie attends
Janice skips and Ellie skips
let A = "Janice attends"
let B = "Ellie attends"
We can rewrite this:
P(A)*P(B|A)
P(A)*P(~B|A)
P(~A)*P(B|~A)
P(~A)*P(~B|~A)

Answer 12

You would read that first line "the probability of A times the probability of B given A happens (is true)"
You would read the third line "the probability of not A times the probability of B given not A (A is not true)"

Answer 13

Anyway, our probabilities are given in the problem:
P(A)*P(B|A) = 62%*100%
P(A)*P(~B|A) = 62%*0%
P(~A)*P(B|~A) = 38%*0%
P(~A)*P(~B|~A) = 38%*100%