Q23 / 54 · JEE Advanced 2016 (Paper 1) · Mathematics

A computer producing factory has only two plants T1 and T2. Plant T1 produces 20% and plant T2 produces 80% of the total computers produced. 7% of computers produced in the factory turn out to be defective. It is known that, 

P(computer turns out to be defective given that it is produced in plant T1)

=10P(computer turns out to be defective given that it is produced in plant T2).

Where, PE denotes the probability of an event E. A computer produced in the factory is randomly selected and it does not turn out to be defective. Then the probability that it is produced in plant T2 is

  • A
    3673
  • B
    4779
  • Correct answer
    C
    7893
  • D
    7583

Solution

PT1=20100

PT2=80100

Let, PDT2=x (where, D represents defective units)

PDT1=10x

PD=7100 (given)

PT1 PDT1+PT2 PDT2=7100

20100×10x+80100×x=7100

x=140

PDT2=140

⇒PD-T2=3940=Probability of not defective, given that it is produced in plant T2

PDT1=1040 ⇒  PD-T1=3040

Now using Bayes' theorem

Probability of computer from T2 given that it is not defective :

PT2D-=80100×394020100×3040+80100×3940=7893

Hence, the correct answer is option: 'C'.

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