数学脑残请你帮看 PREP数学 题

LEDGIRL

如题目，谢谢啦！

crazyxxx

Linda put an amount of money into each of two new investments, A and B, that pay simple annual interest.  If the annual interest rate of investment B is 1.5 times that of investment A, what amount did Linda put into investment A ?

(1)  The interest for 1 year is $50 for investment A and $150 for investment B.

(2)  The amount that Linda put into investment B is twice the amount that she put into investment A.

思路:设A=放在A的存款,B=放在B的存款, Ia为A的利率,Ib为B的利率, Ib =1.5 Ia
条件1. A*Ia = 50, B*Ib = 150,
         A*Ia = 50, 1.5 * B * Ia = 150 -> B * Ia = 100
         得不出A和B
条件2. B = 2A,也得不出A和B
条件1和条件2,
          B = 2A代入 条件一的式子
     A*Ia = 50 没变
     B*Ia = 100 -> 2A*Ia = 100 -> A*Ia = 50
          发现结果代入之后, 还有一个等式未解 A* Ia = 50,那也就得不出A和B的值.

选E

建议这类题目需要好好的化简到最后,看看是不是可以得出结果,经常有这种同比例等式出现的情况,条件看起来多,并不是推出C的充分条件.

crazyxxx

最后一道题目
面积= pi * r^2 - pi* ( r - s )^2, 化简下来就是答案...
个人觉得key point是读题, medallion 是大圆,有有色玻璃小圆和金属边框组成. s是金属边框的宽度,大圆的半径是r.

LEDGIRL

谢谢热血青年，判断的真准确， 强调的地方都是我卡壳的地方。