High School

A quality control inspector selects a sample of 121 items from a shipment for testing. The shipment includes eleven percent defective components. If the policy is to return any shipment with more than five percent defectives, what is the probability that this particular shipment (with eleven percent defectives) will be accepted as good anyway?

Answer :

The probability that a particular shipment (with nine percent defectives) will be accepted as good anyway is 0.0474

Probability of defective item in the shipment, p = 0.09

The policy is to return the shipment if 5% or more are defective. If a sample of 100 is selected, in order to get it accepted not more than 4 items should be found defective.

Calculate the required probability.

P=

{¹⁰⁰C₀ × p⁰ x (1 - p)¹⁰⁰+¹⁰⁰C₁ × p¹× (1 - p)⁹⁹ +¹⁰⁰C₂ × p² ×(1 − p)⁹⁸ + ¹⁰⁰C₃ × p³ ×(1 − p)⁹⁷+¹⁰⁰C₄ × p⁴×(1 − p)⁹⁶ }

Substitute the values.

P = {¹⁰⁰C₀ × 0.09⁰ x (1 - 0.09)¹⁰⁰+¹⁰⁰C₁ × 0.09¹× (1 - 0.09)⁹⁹ +¹⁰⁰C₂ × 0.09² ×(1 − 0.09)⁹⁸ + ¹⁰⁰C₃ × 0.09³ ×(1 − 0.09)⁹⁷+¹⁰⁰C₄ × 0.09⁴×(1 − 0.09)⁹⁶ }

= {¹⁰⁰C₀ × 0.09⁰ x (0.91)¹⁰⁰+¹⁰⁰C₁ × 0.09¹× (0.91)⁹⁹ +¹⁰⁰C₂ × 0.09² ×(0.91)⁹⁸ + ¹⁰⁰C₃ × 0.09³ ×(0.91)⁹⁷+¹⁰⁰C₄ × 0.09⁴×(0.91)⁹⁶ }

= 0.0474

Hence, the probability that a particular shipment (with nine percent defectives) will be accepted as good anyway is 0.0474.

To learn more about statistics and probability,

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