A classroom has 3 electric lamps. From a collocation of 10 electric bulbs of which 6 are good , 3 are selected at random and put in the lamps. Find the probability that the room is lighted.
Select the correct option
A) 1/6	B) 4 / 120	C) 29 / 30	D) 1/9	E) None of these
Explanation :   Out of 10 electric bulbs, 3 are selected in 10C3 ways.   So, number of possible outcomes = T = 10C3 =120.   The room is lighted i.e at least one fo the 3 bulbs chosen at random is a good bulb.   Wherever 'at least one' is present, it is easier to do the problem using complement of the event(i.e room is dark and all 3 bulbs are bad ).   P(room is dark) = F / T = P(none of the bulbs is good)   =&gt; 4C3/120. [since 4 bulbs are bad ].   P (room is lighted )   = 1 - ( 4C3 / 120 ). [ room is lighted if at least one bulb is good ].   or P (at least one)   = 1 - (4 / 120).   = 29 / 30.   Answer : 29 / 30
<result>C</result>
A classroom has 3 electric lamps. From a collocation of 10 electric bulbs of which 6 are good , 3 are selected at random and put in the lamps. Find the probability that the room is lighted.