Question

Word of length 10 are formed using the letters A,B,C,D,E,F,G,H,I,J. Let `x` be the number of such words where no letter is repeated; and let `y` be the number of such words where exactly one letter is repeated twice and no other letter is repeated. The, `y/(9x)=`

Answer 1

Correct Answer - 5
`x = 10!`
`y = ""^(10)C_(1) xx ""^(9)C_(8) xx (10!)/(2!) = 10 xx 9 xx (10!)/(2)`
`rArr" " (y)/(9x) = 10/2 = 5`