Home >All Categories > Science & Mathematics >Mathematics >Open Question alexpptm Member since:June 21, 2008Total points:127 (Level 1)Assume it is known that 10% of calculators from a certain manufacturer are returned for repair while their guarantee is still in effect. If a firm purchased twenty-five calculators for its sales force, what is the probability that five or more of these calculators will need repair while their guarantees are still in effect?
and could you please show how u did it. Thanks!!!Answer Question

by Adrian S Member since:February 23, 2009Total points:4,693 (Level 4)ok. This is a probability problem that is best handled by either the binomial or Bernoulli distribution and I expect you've seen one or the other. p = probability of repair from population = 0.1 and therefore (1-p) = 0.9. Now what you need to do is sum the probabilities of 1, 2, 3 and 4 going in for repair out of the 25 using one of these distributions and subtract from 1.0 to get the probability that 5 or more will have to be repaired.
If you have a TI-83 or above this should be fairly easy to do.If X of the 25 calculators need repair, Xhas binomial distribution with parameters, n=25 and p=0.1.
The pmf is p(x) = 25Cx*0.1^x*0.9^(25-x), x=0, 1, .....25
P[5 or more] = P[X >= 5] = 1 - P[X<5]
= 1 - {p(0) +p(1)+...p(5)}

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