数学题~ 求助

jasper123

195. 18858-!-item-!-187;#058&012264
If w, x, y, and z are integers such that x/w and z/y are integers, is x/w + z/y odd?        B
(1) wx + yz is odd.
(2) wz + xy is odd.
这题应该怎么算呢？

The market value of a certain machine decreased by 30 percent of its purchase price each year. If the machine was purchased in 1982 for its market value of $8000, what was its market value two years later?         C
A 8000                 B 5600                 C 3200                 D 2400                   E 800
这题怎么算出C的？

yongjiew

wz + xy=wy（x/w + z/y）
wz + xy是奇数表明wy与（x/w + z/y）必须全为奇数

xiaoxiaoxxliu

从哪儿可以看出 1/WY是奇数啊

yongjiew

wz + xy=wy（x/w + z/y）   O=O*O
so  x/w + z/y is odd

jasper123

第二题懂了，第一题还是不太明白。。。

yqhpsyche

第一题化简所求就是了，化简后得到（XY+WZ）/WY
根据乘法原理 O*O=O , O*E=E, E*E=E  O：odd   E:Even
这样答案就是B了
至于第一个，代数。 W=X=1 Y=Z=2（反例） insufficient

第二题
Market value in 1982= 8000
Market value in 1983 = 8000- (8000 x 30/100) = 8000-2400= 5600
Market value in 1984 = Market value in 1983 - (30 % of 8000)= 5600-2400 = 3200