问两道prep的数学！

zmyzmy

DS

1.A contractor combined x tons of a gravel mixture that contained 10 percent gravelG,by weight,with y tons of a mixture that contained 2 percent gravel G,by weight,to produce z tons of a mixture that was 5 percent gravel G,by weight.What is the value of x?

(1)y=10

(2)z=16

答案D

我选C了……

2.If P is a positive odd integer,what is the remainder when P is divided by 4?

(1)when p is divided by 8,the remainder is 5.

(2)P is the sum of the squares of two positive integers.

答案D

我选的A

(2)搞不懂。

举个例子

P=3^2+4^2=25时，r为1

p=3^2+5^2=34时，r为2

怎么确定r呢？还是我理解错了？

[此贴子已经被作者于2009/7/20 15:37:16编辑过]

maoruibei

第一题   由题得

10% x =G

2% y = G

5% z = G

只要求出G ，就求出x啦

maoruibei

第二题

2) p=m^2 + n^2

要想 p 还是奇数，那就一定要M N 一个奇 一个偶

那么实验带几个数就得出余数为 1 了

所以要么选B(在不看条件1的时候) 要么选D

maoruibei

如你所推，34还是奇数么？

alan722

2. 1）p=8k+5=4(2k+1)+1  余数是1

   2) P是奇数，那么这两个平方数一个是奇数，一个是偶数 P=（2k+1）^2+(2n)^2=4(K^2+n^2)+4K+1 余数是1

D

xiaoqing508