In a multi-user operating system, 30 requests are made to use a particular resource per hour, on an average. The probability that no requests are made in 40 minutes, when arrival pattern is a poisson distribution, is ______.

1. Ae⁻¹⁵
2. B1 − e⁻¹⁵
3. C1 − e⁻²⁰
4. De⁻²⁰

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Correct answer: D. e⁻²⁰

Explanation

30 requests per hour means λ = 20 in 40 minutes. P(0 arrivals) = e^(−λ) = e⁻²⁰.