Question

Two students are registered for the same class and attend independently of each other, student a 90% of the time and student b 70% of the time. the teacher remembers that on a given day at least one of them is in class. what is the probability that student a was in class that day

Answer 1

The probability of student A is 15/44

Given student A is 70% of time and student B is 60% of time

We need to find the probability of student A

Using formula of conditional probability is P(X/Y) = P(X and Y) / P(Y)

Here X = A and Y = A or B

Therefore,

P(A/A or B) = P(A and (A OR B) / P (A or B)

Now, There is none complement for at least 1

We know that Student A attends 70 % of time

So , his absence is 30% of the time .

Hence the probability of absence is 0.3

Now Considering B in the similar way

We get,

Probability of the absence is 0.4

They are both absent (0.3)(0.4)= 0.12

Here we can say that 12 % of time both are absent

So one or another present on that time is 88%

The probability of present of the time is 0.88

Now calculating the probability,

P(A/A or B) = P(A and (A OR B) / P (A or B)

= 0.3/0.88

= 30/88

= 15/44

Hence the Probability Of A is 15/44

Learn more about Probability here brainly.com/question/24756209

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