SOLUTION: Q.1) The number of entries made in accounts receivable is a poisson distribution with average 2 per day .What is the probability that on a specified day at least 3 entries will be

Question 1180902: Q.1) The number of entries made in accounts receivable is a poisson distribution with average 2 per day .What is the probability that on a specified day at least 3 entries will be received?
Q.2) A company gives an aptitude test to potential employees. The scores are normally distributed with mean 250 and S.D 50.What is the probability that a score is selected at random will be Between 230 and 260.
Q.3) A multiple choice quiz has 400 questions, each question with five possible answers of which one is correct answer. What is the probability that a sheer guess yields exactly 80 correct answers using normal approximation.

Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
Find probability of 0, 1, and 2. Subtract that from 1 and that is probability of at least 3.
P(0)=e^(-2)*2^0/0!=e^(-2)=0.1353
p(1)=e^(-2)*2^1/1!=0.2707
p(2)=e^(-2)*2^2/2!=0.2707
That sum is 0.6770
the answer is 1-0.6770=0.323.
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1-poissoncdf(2,2)=0.323
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this is z=(230-250)/50 or -2/5 and z=(260-250)/50 or +1/5
that is from 0.3446 to 0.5793 or 0.2347.
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the mean is 80 (400*0.2)
the variance is 80*0.8=64
sd is sqrt(V)=8
this would be (79.5-80)/8 +(80.5-8)/8, using the continuity correction factor.
or z= -0.5/8 to +0.5/8, which is -0.0625 to +0.0625.
That is probability 0.0237 on each side or 0.0494 total.
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