PP1-DS-Q172, 173, 176, 180

[mupeane]

172. 17130-!-item-!-187;#058&011022
If m, k, x, and y are positive numbers, is mx + ky > kx + my ?

(1) m > k

(2) x > y

ANS: C

173. 17281-!-item-!-187;#058&011070
If N is a positive integer, is the units digit of N equal to zero?

(1) 14 and 35 are factors of N.

(2) N = (25)(32)(57)(76)

ANS:D

176. 17491-!-item-!-187;#058&011140
If x and y are positive integers, is the product xy even?

(1) 5x - 4y is even.

(2) 6x + 7y is even.

ANS:D

180. 17851-!-item-!-187;#058&011342
Are x and y both positive?

(1) 2x – 2y = 1

(2) x/y > 1

ANS:C

[小花]

[quote="mupeane"]172. 17130-!-item-!-187;#058&011022
If m, k, x, and y are positive numbers, is mx + ky > kx + my ?

(1) m > k
只知道m>K
但不知道 x,y無法比較
(2) x > y
只知道x > y
但不知道 m,k無法比較

(1)(2)合在一起看
把數字帶入算算看(題目已告訴我們全是正整數)
m=4 k=3 x=2 y=1
4*2+3*1>3*2+4*1
11>10
故C

ANS: C

[小花]

173. 17281-!-item-!-187;#058&011070
If N is a positive integer, is the units digit of N equal to zero?

(1) 14 and 35 are factors of N.
14,35是N的因數
N=14*35
把數字乘出來就知道答案
sufficient
(2) N = (25)(32)(57)(76)
把數字乘出來就知道答案
sufficient


ANS:D

我一開始寫這一題選B
因為不確定(1)是否給全部的因數
對答案才知道 題目的意思是給全部的因數

[小花]

176. 17491-!-item-!-187;#058&011140
If x and y are positive integers, is the product xy even?

(1) 5x - 4y is even.

(2) 6x + 7y is even.

ANS:D


(1) 5x - 4y is even
x必須是even, 5x - 4y 才會是 even
已知X=even XY 必為even

(2) 6x + 7y is even
y必須是even,6x + 7y 才會是even
已知y 是even, XY必為even

故D

[小花]

180. 17851-!-item-!-187;#058&011342
Are x and y both positive?

(1) 2x – 2y = 1

(2) x/y > 1

ANS:C

這兒有討論

http://www.formosamba.com/phpBB3/viewtopi ... ositive%3F

對了, 方便後人查詢 , 一個問題發一個帖子會比較好
(雖然我以前也曾這樣過 )

[mupeane]

[[color=darkblue]

因為條件中沒有給到四個數的之前關係，所以不能這樣設

應該是
mx + ky > kx + my =>m(x-y)>k(x-y)
所以由(1)+(2)可得解

[mupeane]

173. 17281-!-item-!-187;#058&011070
If N is a positive integer, is the units digit of N equal to zero?

(1) 14 and 35 are factors of N.
[color=blue]14,35是N的因數
N=14*35
把數字乘出來就知道答案
sufficient[/color]

因為 14和35的最小公倍數是70
所以N是70的倍數

[mupeane]

180. 17851-!-item-!-187;#058&011342

對了, 方便後人查詢 , 一個問題發一個帖子會比較好
(雖然我以前也曾這樣過 )

我知道了，謝謝喔

[puja]

176. 17491-!-item-!-187;#058&011140
If x and y are positive integers, is the product xy even?

(1) 5x - 4y is even.

(2) 6x + 7y is even.

ANS:D


(1) 5x - 4y is even
x必須是even, 5x - 4y 才會是 even
已知X=even XY 必為even

(2) 6x + 7y is even
y必須是even,6x + 7y 才會是even
已知y 是even, XY必為even

故D

這題我補充一下,6x+7y為even 則
6x + 7y 為odd + odd 或 even +even
but 6x 中x為任意數, 則 6x必為 even ,故odd+ odd不合 ,所以可知 7y 為 even---->y=even