考期临近，请教几道math，好心人指教下，谢谢！！！

195.18858-!-item-!-187;#058&012264         

If w, x, y, and z are integers such that w/x and y/z are integers, is w/x+y/z odd?     

(1) wx + yz is odd.

(2) wz + xy is odd.

答案： B。没想通？觉得应该选A。

200.  
19224-!-item-!-187;#058&012506     

If d is a positive integer and f is the product of the first 30 positive integers, what is the value of d ?

(1) 10^d is a factor of f. 

(2) d > 6

答案：C。此题的解法之一是将符合条件的数列出后数出结果，显然...太耗时，特此请教各位大侠，有没有什么简便的方法，谢谢！

177.  
18457-!-item-!-187;#058&011601   （答案错了吧？？？）
     4/7  ???
            

When a certain tree was first planted, it was 4 feet tall, and the height of the tree increased by a constant amount each year for the next 6 years.  At the end of the 6th year, the tree was 1/5 taller than it was at the end of the 4th year.  By how many feet did the height of the tree increase each year?
            

(A)  3/10
            

(B)  2/5
            

(C)  1/2
            

(D)  2/3
            

(E)  6/5

答案：D。觉得应该是答案错了，算了两边都是4/7???

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
            

答案：C。没想通？

203.  
19582-!-item-!-187;#058&012370   

What is the remainder when the positive integer x is divided by 6?

(1)  When x is divided by 2, the remainder is 1; and when x is divided by 3, the remainder is 0.

(2)  When x is divided by 12, the remainder is 3.

答案：D。B很好证明，关键是A？？？

10.
            672-!-item-!-187;#058&000324   

Juan bought some paperback books that cost $8 each and some hardcover books that cost $25 each.  If Juan bought more than 10 paperback books, how many hardcover books did he buy? 

(1)  The total cost of the hardcover books that Juan bought was at least $150.

(2)  The total cost of all the books that Juan bought was less than $260.

答案：C。但

(1)+(2)

    p>10 25h>=150 8p+25h < 260——>6<=h<7.2—>h=6OR7   insufficient ？？？
            

考期临近，盼各位好心人助解，谢谢！！！

172化简得到m（x-y）和k（x-y）的比较问题

第一个条件说明m大于k 第二个条件说明（x-y）大于零，所以成立

最后一道题，如果h=7的话，那么根据第二个条件，8p+25*7<260

那么8p<260-175=85

那么p<10.#￥%%就不满足p》10的条件了

195、条件一，举最简单反例，6/2=3,odd；但6*2=12,even

条件二，先将原式通分=(wz+xy)/xz

如条件二成立，即wz+xy为odd,则原式一定为奇（odd*odd=odd）

200、找5吧……看最多能凑够几个10……2*5，10，15*16，20，25*24，30，共七个……

不确定哦，全凭感觉……没验证过

177、1/5greater than...又没加单位feet,当然是百分比的意思啦，比后者多20%

172、把原式化简下啊^

mx+ky-kx-my=(m-k)x+(k-m)y=(m-k)(x-y)，即问这个式子大于0否

203、根据条件一，x=3m=2n+1

说明m肯定为奇数，3*（2k+1）=6k+3

所以可以算出Remainder为3

10、若h=7得话，p>10的条件就不满足了

lz细心哦

195.18858-!-item-!-187;#058&012264         
            

冒昧的问下，这些符号是什么意思？

冒昧的问下，这些符号是什么意思？