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6. 符合 X^2+Y^2=100的整数解共有多少对? 7. Right triangle PQR is to be constructed in the xy-plane so that the right angle is at P and PR is parrallel to the x-axis. The x-and y-coordinates of P,Q,and Rare to be integers that satisfy the inequalities -4=5,6=16,how many different triangles with these properties could be constructed? 110 1100 9900 10000 12100 8. A box contains 100 balls, numbered from 1 to 100. If three balls are selected at random and with replacement from the box,what is the probability that the sum of the three numbers on the balls selected from the box will be odd? 1/4 3/8 1/2 5/8 3/4 9. 要组成三位电话号码,第一位不能是0或1,三位数中相邻两位不能为同一数. ,求可以组成多少个这样的电话号码? 10. 从1,2,3,4,5,6,7,8,9中选出三个数字组成一个三位数,这个三位数的digits中有两个相同,另一个digit与其它两个都不同,问共有多少个这样的三位数? 72 144 180 216 54 参考答案： 6.解：本题的意为一个半径为10的圆中的整数对有多少对。首先，是一种特殊情况，另四个坐标轴上各有10对解，共41对，对1至7之间的数字而言，任一对均满足条件，则对，对于8，满足条件的有1，2，3，4，5，6六个数，则： | 
