Probability?

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Let x be the number of players

2 C(x,2) - 2 (x - 1) + 4 = 60
2 x (x - 1)/2 - 2x + 2 + 4 = 60
x² - 3x - 54 = 0
(x - 9)(x + 6) = 0
x = 9　　　or　　　-6 ( rejected, since x > 0 )

∴ There were 9 players originally.

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C(x,2)：The number of selection ...... ( select 2 players from x players )
2 C(x,2)：Total number of matches ...... ( originally )
2 (x - 1)：P should play 2 (x - 1) matches ...... ( originally )

( P is the player who was quit after playing 4 matches due to injury. )

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Suppose n ≥ r ≥ 0
0! = 1
n! = n×(n - 1)×(n - 2)...×3×2×1 for n > 0
C(n,r) = n!/[r! (n - r)!]

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