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Data from the Central Hudson Laboratory determined that the mean number of insec

ID: 3202347 • Letter: D

Question

Data from the Central Hudson Laboratory determined that the mean number of insect fragments in 225-gram chocolate bars was 14.4. In a 32-gram bar the mean number of insect fragments would then be 2.05. Assume that the number of insect fragments follows a Poisson distribution. If you eat a 32-gram chocolate bar, find the probability that you will have eaten at least 2 insect fragments. If you eat a 32-gram chocolate bar every week for 9 weeks, find the probability that you will have eaten no insect fragments in exactly 6 of those weeks.

Explanation / Answer

(a)

In a 32 gram bar the mean number of insect fragments would then 2.05.

Here we need to find P (x 2)

P (x 2) = 1 – P (x < 2)

               = 1 – [P (x = 0 ) + P ( x= 1 )]

P (x) = [ (e^-m * m^x) / x! ]   [Poisson distribution]

Mean (m ) = 2.05

p (x = 0) = [ (e^-2.05 * 2.05^0) / 0! ]

               = 0.1287

p (x = 1) = [ (e^-2.05 * 2.05^1) / 1! ]

               = 0.2639

P (x 2) = 1 – P (x < 2)

               = 1 – [P (x = 0 ) + P ( x= 1 )]

               = 1 – [ 0.1287 + 0.2639 ]

               = 1 – 0.3926

               = 0.6074

Answer: 0.6074

(b)

Mean (m) = 2.05 *9

                    = 18.45

P ( x = 6 ) = [ (e^-18.45 * 18.45^6) / 6! ]

                 = 0.0005

Answer: 0.0005