Question

Let letters A,B,C,D,E,F,G be used to form strings of length 4. How many strings of length...

  1. Let letters A,B,C,D,E,F,G be used to form strings of length 4. How many strings of length 4 with repetitions contain A and B. How about without repetitions?

Homework Answers

Answer #1

a) number of total string with repetitions =7^4 =2401

number of total string with repetitions without A =6^4=1296

number of total string with repetitions without B =6^4=1296

number of total string with repetitions without And  B =5^4=625

tehrefore number of total string with repetitions without A or   B =1296+1296-625

=1967

number of total string with A and B =2401-1967=434

b)

without repetitions total number of ways =N(choose 2 from remaining 5 and arrange 4 including A and B )=(5C2)*4! =10*24 =240

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