## 21. A book-shelf can accommodate 6 books from left to right. If 10 identical books on each of the languages A,B,C and D are available, In how many ways can the book shelf be filled such that book on the same languages are not put adjacently.

## 22. In how many ways can the letters of the word ABACUS be rearranged such that the vowels always appear together?

## 23. If the letters of the word **SACHIN** are arranged in all possible ways and these words are written out as in dictionary, then the word **SACHIN** appears at serial number:

**SACHIN**are arranged in all possible ways and these words are written out as in dictionary, then the word

**SACHIN**appears at serial number:

## 24. In how many ways can 3 men and their wives be made stand in a line such that none of the 3 men stand in a position that is ahead of his wife?

## 25. In a cricket match if a batsman score 0, 1, 2, 3, 4 or 6 runs of a ball, then find the number or different sequences in which he can score exactly 30 runs of an over. Assume that an over consists of only 6 balls and there were no extra and no run outs.

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