※ 引述《zoo22 (zoo)》之銘言： These problems belongs to the section of Combination and Permutation : 3.The number of numbers that can be formed by the digits 1,2,3,4,3,2,1. the odd digits are at odd places is given by : A) 430 : B) 215 : C) 93 : D) 36 : E) 18 : Ans: E The numbers of way to plot odd number is at odd position is 4! / 2!2! due to 1 and 3 repeat twice. As for even number, it is 3!/2!1! Multiply these two numbers and there comes the answer --> 6*3=18 : 4. Column A: Number of ways in which 5 differently coloured beads be : strung on a necklace. : Column B: 5!/2 I doubt this answer ABCDE = BCDEA in a necklace (Circular Permutation), therefore, the answer is 5!/5 and then divide by 2(flip the necklace), so it shall be 4!/2.... : 7. A and B are two players of a game. Both of them have same number of coins : before the start of the game. If a person looses the game he gives his : opponent 1 coin and if he wins he gets 1 coin. At the end A has won 4 : games. B has 8 more coins than the nu: mber he had at the start of the : game.Assuming there is no tie in any of the games. Find the number of : games they played. : Ans: 16 B-8 coins ==> it won 8+#-Games A won A won 4, so B won 12 Sum= 16 --

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