How many 4-letter strings can you build using only A, B, C, D? Note: there is no restriction on the number of times that each letter can be used. Each letter can be either not used, or used 1 time, or 2 times, or 3 times, or 4 times. (2) How many 4-letter strings can you build using only A, B, C, D, if each letter has to be used at least once? (3) How many 4-letter strings can you build using only A, B, C, D, if each letter can be used at most twice

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1 To determine the number of 4letter strings that can be built using only the letters A B C and D without any restrictions we need to calculate the to... View the full answer