Let me try to clear this out for you.
You are right, combinations formula is not taking into account orded INSIDE the team thus team 1 of (CD) is not beeing double counted with (DC).
Never the less, when you are selecting 2 from 4, you are considering all possibilities (not double counting inside a team) as follows:
AB
AC
AD
BC
BD
CD
how ever, this is not correct since you need a pair of teams, which means that if you select (AB) as team 1 even without ordering them inside the team, team 2 is already selectes as well (as it will be CD). thus, the first and last option in the list above is in reality the same case and it does not have to be double counted.
hope it helps!
kanikaa9
Krunaal when we use 'combinations', we do so when order doesn't matter, then why are we dividing the result by 2!?
Krunaal
SIndo12
What would be wrong with my approach as 4C2? Pls help
The correct approach includes dividing by 2! => \(4C2 * 2C2 * \frac{1}{2!}\)
We divide by 2! (the factorial of the number of pairs) because the order of the teams does not matter. For example, if the 4 people are labeled 1, 2, 3, and 4, the team-selection (1,2); (3,4) would be considered the same as (3,4); (1,2), as there is no specific order assigned to the teams.
You can practice similar questions here:
https://gmatclub.com/forum/distributing ... 56656.html