The probability that a machine produces a defective item is 0.01. Each item is check as it's produced. Assume these are independent trials and compute the probability that at least 100 items must be checked to find 1 defective item.

answer: 0.3967

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I let x= 100, r= 1,

so

99C0 * (0.01)(0.99)^99, which gives 0.003967

Wrong answer. Explain please.