Question

Consider the following quality control application. Electric fuses produced by Ontario Electricity are packed in boxes of 12 units each. Suppose a quality inspector randomly selects three of the 12 fuses in a box for testing. If the box contains exactly five defective fuses. What is the probability that the inspector will find at least one defective fuse?

7b). Which of these variables are discrete and which are continuous random variables?

a) The number of new professors in the school of Business and Economics

b) The time between buses from the airport to downtown

c) The number of students registered in second year accounting

d) The volume of coffee consumed by the average student during final exam period.

e) The median age of international students in TRU.

Write your answer as either “Discrete” or “Continuous” for question 7b in spaces below

a)

b)

c)

d)

e)

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Answer 1

Let X = the number of defective fuses selected.
h(x; N, n, k) = [ kCx ] [ N-kCn-x ] / [ NCn ]

The probability at least one defective is:

Here N=12,k=5,n=3,x=1
P[X=1] = h(1;12,3,5)
=(5C1)*(7C2)/(12C3)
=5*21/220
=0.477273

The probability at least one defective is 0.477273.

7b). Which of these variables are discrete and which are continuous random variables?

a) The number of new professors in the school of Business and Economics Discrete

b) The time between buses from the airport to downtown. Continuous

c) The number of students registered in second year accounting Discrete

d) The volume of coffee consumed by the average student during the period. Continuous

e) The median age of international students in TRU. Discrete