天山第三套問題求助

woodruff1

1.If wz < 2, is z < 1?

(1) w > 2

(2) z < 2 A:A(為何選A?)

請問在類似的題目中,是否應考慮到w,z為integer?

2.A company has assigned a distinct 3-digit code number to each of its 330 employees. Each code number was formed from the digits

2, 3, 4, 5, 6, 7, 8, 9

and no digit appears more than once in any one code number. How many unassigned code numbers are there?A:6(請問如何解阿?)

3.If the sequence x1 , x2, x3, …, xn, … is such that x1 = 3 and xn +1 = 2xn – 1 for n = 1, then x20 –

x19 =?A: 219

(完全沒思路><)

4.The average (arithmetic mean) of the 5 positive integers k, m, r, s, and t is 16, and k < m

< r < s < t. If t is 40, what is the greatest possible value of the median of the 5 integers?A:18(想不出來)

5.Three printing presses, R, S, and T, working together at their respective constant rates, can do a certain printing job in 4 hours. S and T, working together at their respective

constant rates, can do the same job in 5 hours. How many hours would it take R, working alone at its constant rate, to do the same job?A:20(沒思緒><)

sammen

1.根据条件1W大于2那么题目的等式2边除以W则z<2/w;2/w是可以得出小于1的，是题目要的结果。

2 p(8,3)=336用去330还剩下6个

3我的做法是先算出前4个项（3，5，9，17），看个规律，得出通相1+2^n这样可以算出结果了。

4，根据题目可以得前4个数字得和是40，要中数最大，那么K，M要尽量得小，这样才会使平均值为10，所以k,m分别为1，2，那么R，S得和是37，又S大于R，而且S要尽量得小才可以使R取得最大。

5设他们分别得速度使R S T，那么4（S＋T＋R）＝1；5（S+T)=1根据2个方程可以解得，R为1/20那么R单独要20小时了。

woodruff1

版主强，感谢！！！