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279发行10种不同的邮票，某人有其中的3种。现从这10种中任选2种，问neither of the 2 stamps不在某人所有的3种之内的可能性 ? 答案：C/C=7/15 280. is x^2Y^2? x0。 答案：E 281、=210^t，要求用k、m表示t 答案：k+m+1 =210^t, 10K+M+1=10T 282、直线l，y轴截距2，x轴截距-3，问与l平行的直线 ? 答案：3y-2x=0 同254 283、GWD那道拥有计算机的家庭比例题，答案50% 同304题 感谢ESeraph的补充： Of the families in City X in 1994, 40 percent owned a personal computer. The number of families in City X owning a computer in 1998 was 30 percent greater than it was in 1994, and the total number of families in City X was 4 percent greater in 1998 than it was in 1994. What percent of the families in City X owned a personal computer in 1998? A. 50% B. 52% C. 56% D. 70% E. 74% 284、从6个人中挑3个人组成committee，问有多少种可能? 答案：C=20 285、f=x-1/x，问下面哪一个等于f? 答案：f 同225 第2次出现 286、一个集合由44到54的连续整数 第组成，问随机挑出一个数字，能被7整除的概率 答案：只有49可以被7整除，所以P=1/11 | 
