Question 74040
3 electric lamps are to be fitted in a room. 3 bulbs are chosen at random from 10 bulbs out of which 6 work. What is the chance the room will be lighted? 
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I assume the room will be lighted if at least one of the 3 bulbs selected
is not defective.
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There are 4C3= 4 groups of bulbs that are all defective
There are 10C3 = 120 total number of groups of 3.
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The probability of selecting a group that has at least
one non-defective bulb is 116/120 = 0.966666...
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Cheers,
Stan H.