Prep 2, DS39, 76, 155,跪求解答！

sophia_zx

39.   3150-!-item-!-187;#058&003215

If c and d are integers, is c even?

(1) c(d + 1) is even.

(2) (c + 2)(d + 4) is even.

                                                               C

                                                               C

76.   7085-!-item-!-187;#058&005061

Over a certain time period, did the number of shares of stock in Ruth's portfolio increase?

(1) Over the time period, the ratio of the number of shares of stock to the total number of shares of stocks and bonds in Ruth's portfolio increased.

(2) Over the time period, the total number of shares of stocks and bonds in Ruth's portfolio increased.

                                                                                                                                                                     C

155.
    15795-!-item-!-187;#058&010817

If 500 is the multiple of 100 that is closest to x and 400 is the multiple of 100 that is closest to y, which multiple of 100 is closest to x + y ?

(1) x < 500

(2) y < 400

                                                   E

什么叫500 is multiple of 100?

[此贴子已经被作者于2009/9/12 20:52:45编辑过]

sophia_zx

up,up up

goldensong

39
1) c(d+1) 是even
2) 等价于cd+4c+2d+8 是even, cd是even
合并起来，c和连续2个整数相乘是even,所以c是even

76
1) 股票占(股票+债券)比例上升，不知道总数如何
2) 总数上升，不知道股票比例如何
合并起来，充分

155
举反例吧，
x=401，451是500靠近的数
y=301，351是400靠近的数
靠近x+y的100的multiple有700,800等情况，不充分

sophia_zx

感谢赐教！