(9) Historically we know that 72 out of every 160 purchasing transactions need some form of manual
intervention. On an average day 200 transactions are processed. For any given day, what is the
highest possible number of transactions needing manual assistance? Assume 99% confidence is
required.
A. 100
B. 103
C. 106 CORRECT ANSWER
D. 109
<< 106. We have a Binomial process because manual intervention either happens or it does not
happen. The question also provides details on the best estimate for the “event” probability or
“success” (that manual intervention is required), 72/160 = 0.45.
In Minitab select Calc > Probability Distributions > Binomial. To determine the highest number of
transactions needing assistance, choose inverse cumulative probability and then enter the values
from the question: Trials = 200, Event Probability = 0.45, Input Constant = 0.99. This will return
values of 105 and 106. With 105 the confidence level is 98.6% and with 106 the confidence level
exceeds 99.0%.
In SigmaXL select Insert > Function > CRITBINOM. In this case we know our binomial distribution
is based on a probability of 0.45 and 200 trials. We also know that we seek 99% confidence so our
alpha is 0.99. Excel will return an answer of 106. This is the highest number of transactions we
expect to see with 99% confidence.>>
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