siddhans
Explain in detail... When does order matter ? How do we know that? and when order of selection doesnt matter? I always get confused...
In a race with 10 competitors, the first-place finisher receives a gold medal, the second-place finisher receives a silver medal, and the third-place finisher receives a bronze medal. If there are no ties, in how many different ways may these three medals be awarded?
35
120
720
840
604,800
Here the order matters. Why?
Say there are 3 competitors, A, B, C for 2 medals: Gold(G) & Silver(S)
Winners can be:
G S
---
A B
B A
A C
C A
B C
C B
"A" winning the Gold medal & B winning the silver is different from "B" winning the gold & "A" winning the silver. Thus both scenario should be considered.
A B
B A
So, you choose 2 people out of 3 and rearrange them in 2! way.
\(C^3_2*2!=6\)
Likewise, if there are 10 people; you choose 3 winners first i.e. \(C^{10}_3\)
And then re-arrange those 3!.
Total = \(C^{10}_3*3!=720\)
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If someone says make 2 teams from 3 people A, B, C, then \(C^3_2\) suffices.
Note:
Having a team that contains A and B
IS NO DIFFERENT FROM
Having a team that contains B and A
Thus, order won't matter there.
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