A pathologist has been studying the frequency of bacterial colonies within the field of a microscope using samples of throat cultures from healthy adults. Long-term history indicates that there is an average of 2.74 bacteria colonies per field. Let r be a random variable that represents the number of bacteria colonies per field. Let O represent the number of observed bacteria colonies per field for throat cultures from healthy adults. A random sample of 100 healthy adults gave the following information. r 0 1 2 3 4 5 or more O 13 13 32 17 17 8 (a) The pathologist wants to use a Poisson distribution to represent the probability of r, the number of bacteria colonies per field. The Poisson distribution is given below. P(r) =  e−λλr r! Here λ = 2.74 is the average number of bacteria colonies per field. Compute P(r) for r = 0, 1, 2, 3, 4, and 5 or more. (Round your answers to three decimal places.) P(0) =   P(1) =  P(2) =  P(3) =  P(4) =  P(5 or more) =  (b) Compute the expected number of colonies E = 100P(r) for r = 0, 1, 2, 3, 4, and 5 or more. (Round your answers to one decimal place.) E(0) =   E(1) =   E(2) =  E(3) =  E(4) =  E(5 or more) =  (c) Compute the sample statistic  χ2 =    (O − E)2 E      and the degrees of freedom. (Round your test statistic to three decimal places.) d.f. =   χ2 =

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A pathologist has been studying the frequency of bacterial colonies within the field of a microscope using samples of throat cultures from healthy adults. Long-term history indicates that there is an average of 2.74 bacteria colonies per field. Let r be a random variable that represents the number of bacteria colonies per field. Let O represent the number of observed bacteria colonies per field for throat cultures from healthy adults. A random sample of 100 healthy adults gave the following information.

r 0 1 2 3 4 5 or more
O 13 13 32 17 17 8
(a) The pathologist wants to use a Poisson distribution to represent the probability of r, the number of bacteria colonies per field. The Poisson distribution is given below.
P(r) = 
e−λλr
r!
Here λ = 2.74 is the average number of bacteria colonies per field. Compute P(r) for r = 0, 1, 2, 3, 4, and 5 or more. (Round your answers to three decimal places.)
P(0) =  
P(1)
P(2)
P(3)
P(4)
P(5 or more)

(b) Compute the expected number of colonies E = 100P(r) for r = 0, 1, 2, 3, 4, and 5 or more. (Round your answers to one decimal place.)
E(0) =  
E(1) =  
E(2)
E(3)
E(4)
E(5 or more)

(c) Compute the sample statistic 
χ2 = 
 
(O − E)2
E
 
 
 and the degrees of freedom. (Round your test statistic to three decimal places.)
d.f. =  
χ2 =  


 

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