Total number of five letter strings formed by A,B,C and D with repetitions allowed
={4x4x4x4x4 = 4 power 5 = 1024
Now, fix BAD in a string at one place then we have 2 more places to be filled with 4 letters, total number of such strings
=4x4=16
Here, BAD can be at any of the 3 positions,
Hence the total number of strings with BAD in it
= 3 x 16=48
Now, The total number of strings not containing BAD
=1024-48
=976
Using 26 letters, the number of 5-letter words that can be formed when the letters are different is determined as follows: 26P5 = 26 × 25 × 24 × 23 × 22 = 7883600 different words.
Learn more about five-letter strings here:https://brainly.com/question/27134945
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