1.

In how many ways 4 mathematics books, 3 physics books, 2 chemistry books and 1 biology book can be arranged on a shelf so that all books of the same subjects are together.

Answer»

Number of maths book = 4 

Number of physics books = 3 

Number of chemistry books = 2 

Number of biology books = 1 

Since we want books of the same subjects together, we have to treat all maths books as 1 unit, all physics books as 1 unit, all chemistry books as 1 unit and all biology books as 1 unit. Now total number of units = 4 

They can be arranged in 4! ways. After this arrangement. 

4 maths book can be arranged in 4! ways 

3 physics book can be arranged in 3! ways 

2 chemistry book can be arranged in 2! ways and 1 biology book can be arranged in 1! way 

∴ Total Number of arrangements 4! 4! 3! 2! = 6912



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