You are taking a chemistry test and are asked to list the first ten elements in order as they appear in the periodic table. Suppose you have no idea of the correct order and simply guess. In how many orders could you list the elements?

Question

jamesj · Answer

In the first place you 10 choices; then for the second place you have 9 choices; hence so far you 10 times 9 = 90 choices.

In the third place, you have 8 choices and so on.

Hence in total you have 10.9.8.7.6.5.4.3.2.1 choices.  We write this number as 10!

Your calculator has a button for it or you can now calculate it.

anonymous · Answer

Thanks! That's the answer the book gave me, but I didn't know how it got there, and I have a quiz tomorrow. I appreciate it!