Probability/Additional Topics in Probability and Counting Question 44 Defective Units

A shipment of #a microwave ovens contains #b defective units.  In how many ways can a restaurant buy three of these units and recieve:

  1. no defective units?
    {#1}

  2. one defective unit?
    {#2}

  3. at least two nondefective units?
    {#3}

  4. What is the probability of the restaurant buying at least two defective units?
    {#4}
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