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1. 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.
The subsequent places can be filled in 3 ways each.
Hence, the number of ways
= 4 × 3 × 3 × 3 × 3 × 3
= 4 × 35
Solution:
First place can be filled in 4 ways.The subsequent places can be filled in 3 ways each.
Hence, the number of ways
= 4 × 3 × 3 × 3 × 3 × 3
= 4 × 35