Question 1207619
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I have 3 different mathematics textbooks, 2 different psychology textbooks, 
and 2 different chemistry textbooks. In how many ways can I place the 7 textbooks 
on a bookshelf, in a row, if all three mathematics textbooks must be together?
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We start the solution, considering 3 Math textbook as one object. 
We have then 5 different objects, at all, and 5! = 120 possible
permutations for them.


Then we multiply 5! by 3! = 6, the number of permutations inside the set of 3 Math textbook.


Thus we come to the 


<U>ANSWER</U>.  There are 5!*3! = 120*6 = 720 different arrangements of the textbooks 
         on a bookshelf under the given restriction.
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Solved.