A carton contains 25 bulbs , 8 of which are defective. What is the probability that if a sample of 4 bulbs is chosen , exactly 2 of them will be defective ?
Hi sukhman,
What is the source of this question? And where are the answer choices? These numbers are rather large for what the GMAT writers would put into a question of this type, which makes me think that it's not a representative question.
The solution has to take into account the number of defective and non-defective bulbs as well as the total bulbs. In addition, ANY 2 of the 4 bulbs could be defective, so you have to factor in the combination formula.
It would be this: [spoiler](4c2)(8x7x17x16)/(25x24x23x22)[/spoiler]
This math is something the GMAT would NOT ask you to solve.
GMAT assassins aren't born, they're made,
Rich
