A) \[{{(n-1)}^{r}}\]
B) \[{{r}^{n-1}}\]
C) \[{{n}^{r-1}}\]
D) \[{{(r-1)}^{n}}\]
Correct Answer: D
Solution :
[d] Number of copies of a book that can be selected are 2 or 3 or 4 ... or r. Thus, for each book we have \[(r-1)\] ways. \[\therefore \] Total number of ways \[={{(r-1)}^{n}}\]
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