Question

Just carpet has eight different quality grades of carpeting. Three types are being selected for a corporate test on durability. how many different samples of size 3 can be taken without replacement? how many different samples of size 5 can be taken without replacement?

Answer 1

When we have a set of N elements, the number of combinations of K elements (such that N ≤ K) from these N elements is:

`C(N, K) = (N!)/((N - K)!*K!)`

Then if we have 8 different types of carpet, and we want to see how many different samples of 3 types we can choose, we just need to replace N by 8, and K by 3 in the above equation:

`C(8, 3) = (8!)/((8 - 3)!*3!) = (8!)/(5!*3!) = (8*7*6)/(3*2) = 56`

So there are 56 different samples.

Now we can do the same, but this time we want to use 5 types of carpet, then we will have K = 5.

`C(8, 5) = (8!)/((8 - 5)!*5!) = (8!)/(3!*5!) = 56`

Again, we have 56 different samples.