Question 1183044:  How many ways can we select three books each from a different subject from a set of six distinct history books, nine distinct classics books, seven distinct law books, and four distinct education books? 
 Answer by ikleyn(52903)      (Show Source): 
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How many ways can we select three books each from a different subject  
from a set of six distinct history books, nine distinct classics books,  
seven distinct law books, and four distinct education books? 
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We have the sets 
    - H (history, 6 books)
    - C (classic, 9 books)
    - L (law, 7 books)
    - E (educational, 4 books).
We can select 3 different subject books from the set H U C U L by 6*9*7 = 378 ways.
We can select 3 different subject books from the set H U C U E by 6*9*4 = 216 ways.
We can select 3 different subject books from the set H U L U E by 6*7*4 = 168 ways.
We can select 3 different subject books from the set C U L U E by 9*7*7 = 252 ways.
Doing this way, we counted all possible combinations of 3 different subject books.
So, the answer to the problem's question is the sum  378 + 216 + 168 + 252 = 1014 different ways.
 
Solved and carefully explained.
 
 
 
 
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