Question

SAT数学题 帮忙看下~~~~~~~~~~~~~(4)

3. Michell has 20 cons in her purse. There are only 10 pence, 20 pence, and 50 pence coins and total value of the money is 500 pence. If she has more 50 pence coins than 10 pence coins, how many 10 pence coins does she have?
A) 1 B) 5 C) 2 D)7 E) 9
******** 这题我是这么做的 用的xyz
50 p——x 20p——y 10p——z
x+y+z=20 x=x >0
50x+20y+10z=500 → y=30-x >0 → 3<x<5 → x=4 → y=16
x>z z=3x-10 >0 z=2
有没有其他简便点的方法呢？或是试数？ 可我感觉盲目的试数会更麻烦啊

12. For different numbers A,B,C and D are chosen from the set { -4 , -3/2 , -1 , 0 , 5/8 , 1 , 4 , 7 }. What is the smallest possible value of the sum (A/B) + (C/D) ?
A) -45/23 B) 30/26 C) 67/5 D) 45/23 E) -67/5
********* 这题该怎么做？只能用试数的方法么 就没有什么其他比较清楚的方法吗

14. Joe and Jim are next door neighbors. Ted lives 4 miles from them. Each golf day, Ted drives to their houses and they all drive together, in one of their cars, 11 miles to a golf course. After golfing, they return to Joe and Jim’s houses and then Ted drives home. They agree to take turns driving in such a way that total amount of driving from their houses should be the same for all. What is the fewest number of golf days that would make this possible and how many of these says would Ted drive to the golf course?
A) 10, 1 B) 10, 2 C) 11, 1 D) 11, 2 E) 11, 3
********** 彻底没看懂....

这个答案是 3.C 12.E 14.C
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Answer 1

上两题我同意楼上的意见。
最后一题，楼上的译文是对的。可以设一共打x天，其中ted开车的天数是y。则有
8x+22y=22（x-y）/2
因为ted每次都要自己开车到人家。
得到x=11y。所有最少要打11次球，其中1天由ted开车去球场。大家开车的里程刚好相同。

Answer 2

3、
貌似只能这样做。你可以设x,y，和20-x-y，气氛上少个未知数的样子。
12、
就试就行了，反正没几个数。
也不能盲目的试，譬如要最小的话，AB，CD得相互异号，且均不为零。两个分数都是最小的负数的时候就行了。
14、
翻译：Joe和Jim是邻居，而Ted住在4英里之外。他们一起打高尔夫的那天，Ted先开车到Joe和Jim那，他们仨再坐一辆车一块儿开11英里去打高尔夫。打完之后，他们再先一起返回Joe和Jim家，然后Ted再自己开车回家。他们约好轮流开车，这样没个人从自己家开的总距离是一样的。那么想达到这个目的，他们最少要去打多少天高尔夫，这其中ted要开多少天车。