请教几道机考题，谢谢

yoo_hoo

1.Which of the following coordinates are on the line segment connecting (5,6) and (21,18)?

A (9,9)    B (12,12)    C (13,13)    D (12,13)   E (16,15)     答案为什么是A呢？想不明白

2.A family of 4 is at a restaurant with 6 choices on the menu.  If nobody orders the same meal, how many possible combinations of meals could they order?

A) 15     B) 30      C) 60     D) 180     E) 360        答案为什么是E呢， 不应该是C64=15吗？

3.There are 150 students at Seward High School. 66 students play baseball, 45 play basketball, and 42 play soccer. 27 students play exactly two sports, and three students play all three of the sports. How many of the 150 students play none of the three sports?

A) 0    B) 27   C) 30    D) 99     E) 78  答案是C，可我做的是150-（66+45+42-27-3）=27？请问我那里错了，为什么呢？

谢谢各位了。

ssss

1.Which of the following coordinates are on the line segment connecting (5,6) and (21,18)?

列出方程：y-5=(12/16)*(x-5) 将（9，9）带入，符合，所以选A

注：12/16是斜率，是(18－6)/(21-5)这样算出来的

2.A family of 4 is at a restaurant with 6 choices on the menu.  If nobody orders the same meal, how many possible combinations of meals could they order?

应该是C64*P44    在6个菜中选出来的4个菜要分给4个人，有P44种分发

3.There are 150 students at Seward High School. 66 students play baseball, 45 play basketball, and 42 play soccer. 27 students play exactly two sports, and three students play all three of the sports. How many of the 150 students play none of the three sports?

看下图，图中红色的部分是27。你的算式多减了一个3。

[attachimg]14733[/attachimg]

yoo_hoo

太感谢了，解释的如此透彻明了，谢谢。