求助几道数学题，万分感谢！

scarlett006

1、If n is a multiple of 5 and n=(p^2)*q, where p and q are prime numbers, which of the following must be a multiple of 25?
A. P^2     B.q^2    C.p*q   D.(p^2)*(q^2)   E.(p^3)*q

答案是C，俺不懂啊

2、If x and y are integers greater than 1. Is x a mupltiple of y?
条件一：3y^2+7y=x
条件二：(x^2)-x is a multiple of y

答案是A，依旧不懂啊

3、A certain business produced x rakes each month from November through February and shipped x/2 rakes at the begining of each month from March through October. The business paid no storage costs for the rakes from Noveber through February, but it paid storge costs of $0.1 per rake each month from March through October for the rakes that had not been shipped. In terms of x, what was the total stortage cost, in dollars, that the business paid for the rakes for the 12 months from November through October?
A.0.4x
B.1.2x
C.1.4x
D.1.6x
E.3.2x

答案是C，不懂呃。。

masushuang

第二题：

问题可以restate为：Is x=ay? 通过移项用y来表达x。

(1) 3y^2+7y=x, then y(3y+7)=x, i.e. x=y(3y+7). Because y is an integer, 3y+7 is an integer, then x=ay 's a=3y+7(integer) , which means x is a multiple of y.
(2) (x^2)x=by, so x(x-1)=by, then x=by/(x-1), then (b/x-1)y, x-1 is an integer, but you don't know whether b/(x-1) is an integer, so we're not sure whether x is a multiple of y.

答案：A

masushuang

我也觉得第一题是D。p,q中必有一个为5。

honpont2013

第三题  选C   就是简单的计算   从3月份起  除去月初发货的 和十月最后一次发货的  每个月要交的仓储费从3月开始是  3.5  3 2.5  2 1.5 1 0.5   相加*0.1   =1.4

honpont2013

第一题选D    n是5的倍数只能说明p或者q有一个是5  C不能确定，但是D 肯定是25的倍数


第二题  选A 条件一：3y^2+7y=x    移项就好  y(3y+7)=x  所以x must be the multiple of y
                    条件二：(x^2)-x is a multiple of y       x(x-1)=y   只能确定y是x的倍数

llqq1220

第三题应该是（0.35+0.05）乘以0.05然后整个除以7.。。就是答案

LuckyStars

第三道题是等差数列

不过我用最愚蠢的办法，从三月一直加到10月，也加出来就是1.4x

答案没问题

veralove3271

第三题：FEB-NOV总产量4x,因为MAR初就开始SHIP所以 开始收费库存是7x/2，然后是6x/2......一直到x/2。它们的和乘以0.1即为答案。

polaris16251

第一题答案是D啊。p和q中至少有一个是5.
veralove3271 发表于 2012-7-14 15:52

我也觉得第一题，n是5的倍数只能说明p或者q有一个是5

所以，要是25的倍数，必须是p^2乘以q^2

veralove3271

第一题答案是D啊。p和q中至少有一个是5.