For a segment of a radio show a DJ can play 9 records. If there are 12 records to select from, in how many ways can the program for this segment be arranged.

Question

parthkohli · Answer

See, we choose 9 from 12, so it'd be 12 choose 9 aka 12c9.

parthkohli · Answer

Do you know what combinations are?

jim_thompson5910 · Answer

This is similar to the last problem

There are 12 choices for the first slot

There are 11 choices for the second slot

etc etc

until you get to 3 choices for the 9th slot

parthkohli · Answer

Basically, nCr is:

$\Large \color{MidnightBlue}{\Rightarrow {n! \over (n - r)! r!} }$

anonymous · Answer

yes its sure been a while since i dont problems like this. thanks for the replys.

anonymous · Answer

what do i multipy thats whats throwing me off

anonymous · Answer

$$ \large \binom{12} 9 = \binom{12} 3= 220 $$