



 
Hi Carole, I am going to do a similar problem.
If I start to write down an arrangement I need to choose a first letter. There are 3 choices. Once I write down the first letter I need to decide on a second letter. Since one has already been chosen there are 2 choices for the second letter. Thus there are 3 × 2 = 6 ways to write the first two letters. Once I have written down the first two letters there is only one possibility for the third letter and hence there are 6 possible arrangements of the letters a, b and c. Here they are in a list
But you have two digits the same so let me make two of the letters the same.
Notice that in the list generated in the first problem the arrangements go together in pairs. Every arrangement has a twin where the placement of the a and c are reversed. If you write a in place of each c the list becomes
which collapses to
Since the list collapsed in pairs the answer to question 2 is 3, half the answer to question 1. Now try your problem,  


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