Exercise 1: Exactly 4 Incidents With lambda=2 — Possible Solution
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GIVEN
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lambda = 2, k = 4

STEP 1: lambda^k
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2^4 = 16

STEP 2: e^-lambda
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e^-2 ~= 0.1353

STEP 3: k!
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4! = 4 x 3 x 2 x 1 = 24

STEP 4: COMBINING
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P(X=4) = (lambda^k x e^-lambda) / k!
        = (16 x 0.1353) / 24
        ~= 2.165 / 24
        ~= 0.0902 (about 9.02%)

WHY THIS WORKS AS AN ANSWER
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Each of the three terms in this chapter's own Poisson formula is
computed separately - the rate raised to the observed count, the
decay factor e^-lambda, and the normalizing factorial - before being
combined, matching the chapter's own worked request-arrival example
step by step (which used the same lambda=2 and produced the identical
numeric result for k=4, since it's the same calculation).