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Basics of combination

Srijita Banerjee
B.Tech in Biotechnology\singer\loves teaching\public speaker\peer educator\Bengali

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1. COMBINATROICS: Combination GRE QUANTS SRIJITA BANERJEE https://unacademy.com/user/mampi

2. . Suppose we have 10 employees and out of them we need to select 5 for a particular project 02

3. . Suppose we have 10 employees and out of them we need to select 5 for a particular project. Now, suppose (X C B G H have been selected 02

4. . Suppose we have 10 employees and out of them we need to select 5 for a particular project. Now, suppose (X C B G H have been selected All that matters over here is who has been selected and now how or in what way they have been selected. 02

5. . Suppose we have 10 employees and out of them we need to select 5 for a particular project. Now, suppose (X C B G H have been selected All that matters over here is who has been selected and now how or in what way they have been selected. Ultimately, in combination only the final group matters and the arrangements or the stages doesn't 02

6. How is it represented?? 02

7. How is it represented?? . If there are n total items or individuals r is the number that is needed Then, combination is usually given by nCr 02

8. Let us consider a situation. 02

9. Let us consider a situation. There are people and out or these 7 people we have to select one 02

10. Let us consider a situation. There are people and out or these 7 people we have to select one So basically it is 7C1 02

11. Let us consider a situation. There are people and out or these 7 people we have to select one So basically it is 7C1 But we can choose1out of 7 in 7 different ways So, 7C1 7 02

12. What if the selection is 3 out of 7 It becomes 7C3. Now if you look into this thing carefully, you'll be able to notice that when we are creating a group of three out of Test @ero veis on the other hand creating a group of the rest (leftovers). 02

13. What if the selection is 3 out of 7 It becomes 7C3. Now if you look into this thing carefully, you'll be able to notice that when we are creating a group of three out of rest (leftovers). Which is nothing other than 7C4 So, in other ways we can conclude 7C3-7C4 Test @ero veis on the other hand creating a group of the 02

14. In general, when we create a pool of r out of n we automatically create a group of (n-r) items which are left behind.

15. In general, when we create a pool of r out of n we automatically create a group of (n-r) items which are left behind. So, always: nCr nC(n-r)

16. Now let us discuss how to calculate 7C3: If we consider a group of 7, how many different way can we select them here (if we want to select 3) 7*6*5 (using FCP) This would obviously be the case if the order was taken into consideration Here the order doesn't mater So, we need to divide by 3! Ans: (7 6 5)/(3!) 02

17. In a library there a 12 subject books for person Al. Although the rules of library say that he could only take 4 books at a time. In how many different ways can Al make sets of 4 books out of the 12 books? 02

18. In a library there a 12 subject books for person Al. Although the rules of library say that he could only take 4 books at a time. In how many different ways can Al make sets of 4 books out of the 12 books? 12C4 (12*11*10*9)/(4!) = 495 02