Answer :
Answer: 475,254
This is one single number and not two separate numbers.
Delete the comma if your teacher requires it.
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Explanation:
I'm assuming letters can repeat.
There are 26 letters in the English alphabet.
There are,
- A = 26^4 = 456,976 strings of length four
- B = 26^3 = 17,576 strings of length three
- C = 26^2 = 676 strings of length two
- D = 26 strings of length one
Overall, there are A+B+C+D = 456,976+17,576+676+26 = 475,254 strings of length four or less.