a. How many possible selections are there of four letters?

b. How many arrangements are there of four letters?

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I know for part (a) E and S are special but I only know how to work out the answer if

*one*letter is special.

QUESTION: Eight cards are selected with replacement from a standard pack of 52 playing cards, with 12 picture cards, 20 odd cards and 20 even cards.

a. How many different sequences of eight cards are possible?

b. How many of the sequences in part (a) will contain three picture cards, three odd numbered cards and two even numbered cards?

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I've tried part (a) almost 10 times and my answer is still incorrect.