Q45 / 91 · KVPY 2018 (SB/SX) · Mathematics

The probability of men getting a certain disease is 12 and that of women getting the same disease is 15. The blood test that identifies the disease gives the correct result with probability 45. Suppose a person is chosen at random from a group of 30 males and 20 females, and the blood test of that person is found to be positive. What is the probability that the chosen person is a man?

  • Correct answer
    A
    75107
  • B
    35
  • C
    1519
  • D
    310

Solution

We have 30 males and 20 females.

Pmales=3050=35

Pfemales=2050=25

Figure

Required probability =1+31+3+5+7

=35×12×45+35×12×1535×13×45+35×12×15+25×15×45+25×45×15

=15501550+16125=75107

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

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