I am having trouble with a chemistry homework problem.  The question
is, how many moles are represented in 100 molocules (exactly) of H2O? 
The answer I got is 2e-22, but this answer is wrong.  Please explain
to me (i) the step by step process to get the right answer, (ii) what
you think I might have done wrong, and (iii) what the right answer is.

Thank you in advance for your help.  It is very much appreciated.

1 mole of anything is 6.022 x 10^23
1 molecule is 1/6.022 x 10^23 mol
100 molecules is 100/6.022x10^23 mol
This equals 1.66 x 10^-22 mol

You may well have used the correct method, and obtained the correct
answer, but expressed it only to one significant figure.

Thanks for your response.  You were right about the significant figure.  

Thanks.