Question 93528
Permutations 
1. taking all 7 letters at a time---: 7!
2. taking 5 letts at a time---: 7!/(7-5)!
3. taking 4 letters at a time---: 7!(7-4)!
4. taking 3 letters at a time 
Question: in how many ways can 12 books be displayed on a shelf if the given number of books are available? 
5. 12 books-- : 12!
6. 14 books-- : 14!/(14-12)!
7. 15 books-- : 15!/(15-12)!
8. 20 books 
Question: Find the number of permutations of the letters in each word. 
9. geometry---: 8!/2!
10. algebra--: 7!/2!
11. addition--: 8!/[2!*2!]
12. calculus--: 8!/[2!*2!*2!]
13. mathematics
14. arithmetic