Question Details

Three students S1, S2, and S3 are given a problem to solve. Consider the following events:

U: At least one of S1, S2, and S3 can solve the problem,

V: S1₁ can solve the problem, given that neither S2 nor S3 can solve the problem,

W: S2 can solve the problem and S3 cannot solve the problem,

T: S3 can solve the problem.


For any event E, let P(E) denote the probability of E. If


P ( U ) = 1 2 , P ( V ) = 1 10 , P ( W ) = 1 12


Then P(T) is equal to


Options

A

13/36

B

1/3

C

19/60

D

1/4

Show Answer

Correct Answer :

Option A

13/36

13/36

Solution :

Let S1, S2, and S3 be the independent events that students 1, 2, and 3 solve the problem, respectively. Let their probabilities be denoted as:

P(S1)=p1, P(S2)=p2, and P(S3)=p3.

The events given in the problem can be expressed as follows:

1. Event U: At least one of the students can solve the problem.
The probability of event U is the complement of none of the students being able to solve the problem:
P(U)=1-P(S1'S2'S3')=1-(1-p1)(1-p2)(1-p3)
Given that P(U)=12, we have:
(1-p1)(1-p2)(1-p3)=12 (Equation 1)

2. Event V: S1 can solve the problem, given that neither S2 nor S3 can solve the problem.
P(V)=P(S1|S2'S3')
Since the events are independent, the conditional probability simplifies to:
P(V)=P(S1)=p1
Given that P(V)=110, we get:
p1=110

Substituting p1=110 into Equation 1:
(1-110)(1-p2)(1-p3)=12
910(1-p2)(1-p3)=12
(1-p2)(1-p3)=12×109=59 (Equation 2)

3. Event W: S2 can solve the problem and S3 cannot solve the problem.
P(W)=P(S2S3')=p2(1-p3)
Given that P(W)=112, we have:
p2(1-p3)=112 (Equation 3)

4. Finding P(T):
We need to find the probability of event T, which is P(S3)=p3.
Let us expand Equation 2:
(1-p2)(1-p3)=1-p3-p2(1-p3)=59

Substitute the value of p2(1-p3) from Equation 3 into the expanded expression:
(1-p3)-112=59
1-p3=59+112

Finding a common denominator (36):
1-p3=2036+336=2336
p3=1-2336=1336

Therefore, the probability P(T) is equal to 1336.

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