Permutations or combinations? Combinations Answer: 816
Practice makes perfect
We want to find how many ways there are to select 3 backup singers out of 18 who try out. Note that, in this case, the order is not important. Thus, the situation involves combinations. To calculate the answer, we will use the formula for combinations of n singers taken r at a time.
_n C_r = _n P_r/r! ⇔ _n C_r = n!/(n-r)!r!
In our exercise, n= 18 and r= 3. Let's substitute these values into the above formula.
