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GATE 2024 ST – Question 40

Standard Univariate Distributions · Continuous Distributions · 2 marks · Multiple choice

Checkout service times are independent exponential with density e^(−x/10)/10,x≥0. On arrival one customer is already being served and has spent five minutes there. Find the probability your remaining queue time plus your own service exceeds 15 minutes.

  1. (5/2)e^(−3/2)
  2. (3/2)e^(−3/2)
  3. (3/2)e^(−5/2)
  4. (5/2)e^(−5/2)

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Correct answer: (A) (5/2)e^(−3/2)

Explanation

Memorylessness makes the current customer’s remaining time exponential of mean 10, unaffected by the elapsed five minutes. Add your independent service of the same law: total is gamma with shape 2,rate 1/10. Survival at 15 is e^(−15/10)(1+15/10)=**(5/2)e^(−3/2), A**.

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