A shopkeeper has 13 washing machines out of which 5 are defective. A customer buys 3 washing machine. What is the probability that exactly one machine is defective?
(a) 1/20 (b) 1/5 (c) 70/143 (d) 35/143

• 5 are defective and (13-5) are not defective so out of 3 machines 1 from defective and 2 from not defective.
  (5C1x8C2)/13C3 = 70/143
• 7 years agoHelpfull: Yes(2) No(1)
• answer is (c) 70/143
  explanation:-
  total=13
  defective=5
  not defective=8
  so, he bought 3 machines, out of which 1 must be defective and 2 be non-defective.
  so, he must bought 2 from 8(non-defective machines) and 1 from 5(defective machines).
  so, answer is:-
  (8 C 2 * 5 C 1) / 13 C 3 =70/143 is the answer.
• 7 years agoHelpfull: Yes(0) No(0)
• sorry, answer is (d)35/143
  it was my calculation mistake.
• 7 years agoHelpfull: Yes(0) No(0)
• 8C2*5C1 / 13C3 = 70/143
• 5 years agoHelpfull: Yes(0) No(0)