This was an explanation from MGMAT that I'm having trouble trying to understand...
Q: If three of seven standby passengers are selected for a fight, how many different combinations of standby passengers can be selected.
The way I tried to solve it:
You have 7 to choose from for the first stand by slot.
7!
You then have 6 to choose from for the 2nd stand by slot.
6!
Finally, you have just 5 to choose from for the last stand by slot.
5!
Therefore, ANS is =7!6!5!
However, this is wrong.
The correct answer is (7!)/(3!*4!)
Why? The book tries to explain it using the Anagram style of solving problems. I still, conceptually, don't understand why you would have to divide it by 3!*4!. They say that this is a situation where the "chosen ones" are indistinguishable. What do they mean by that?
Confusing.
Q: If three of seven standby passengers are selected for a fight, how many different combinations of standby passengers can be selected.
The way I tried to solve it:
You have 7 to choose from for the first stand by slot.
7!
You then have 6 to choose from for the 2nd stand by slot.
6!
Finally, you have just 5 to choose from for the last stand by slot.
5!
Therefore, ANS is =7!6!5!
However, this is wrong.
The correct answer is (7!)/(3!*4!)
Why? The book tries to explain it using the Anagram style of solving problems. I still, conceptually, don't understand why you would have to divide it by 3!*4!. They say that this is a situation where the "chosen ones" are indistinguishable. What do they mean by that?
Confusing.
