Ira S. answered • 04/26/15

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The counting principle says that you can take the number of ways that each individual event can occur,,,,and multiply them.

So

a) 9*26*26*26*10*10*10=158,184,000

b) 1*26*26*26*10*10*1 =1,757,600

c) 9*26*25*24*9*8*7 =70,761,600

For Part c, since I had 9 choices for the first number, that leaves me 9 choices for the number in the fourth slot....and then i"ve already used 2 numbers, leaving me with 8 numbers for the next slot and 7 for the final slot. For the letters, I had 26 choices for the first, but since ai used one and can't repeat, I have 25 for the net....and now that I used 2 letters already, I have 24 choices for the last letter.

Hope this helped.