Q32 / 75 · JEE Main 2020 (07 Jan Shift 2) · Mathematics

In a workshop, there are five machines and the probability of any one of them to be out of service on a day is 14 . If the probability that at most two machines will be out of service on the same day is 343k, then k is equal to

  • Correct answer
    A
    178
  • B
    174
  • C
    172
  • D
    4

Solution

Given $n=5, p=\frac{1}{4}$ and $q=1-p=\frac{3}{4}$

Required probability = when no machine has fault + when one machine has fault + when two machines have fault.

=C05345+C1514344+C25142343

=2431024+4051024+2701024=9181024=459512=27×1764×8

⇒343×k=343×178

∴k=178

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

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