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. Choose the correct choice from the following choices
A) 1 / 6	B) 4 / 120	C) 29 / 30	D) 1 / 9	E) none of these

Rationale: explanation : out of 10 electric bulbs , 3 are selected in 10 c 3 ways . so , number of possible outcomes = t = 10 c 3 = 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 ) = > 4 c 3 / 120 . [ since 4 bulbs are bad ] . p ( room is lighted ) = 1 - ( 4 c 3 / 120 ) . [ room is lighted if at least one bulb is good ] . or p ( at least one ) = 1 - ( 4 / 120 ) . = 29 / 30 . answer : c
Answer: C