两道PERP数学。。请大家帮忙解答一下.

狮子marilyn

1. n,y都是正整数，450y=n^3,  which of the followling is integer?

I     y/(3*2^2*5)

II    y/(3^2*2*5)

III   y/(3*2*5^2)                 答案是  only I

2.there are 60 animals on the farm,2/3 are either pigs or cows,how many are cows?

(1)the farm has more than twice as many cows as it has pigs

(2)the farm has more than 12 pigs.

先谢谢大家了`~！

in2deep

1。450y=n^3相当于2*（5^2）*（3^2）y=n^3

n是正整数，则y应该包含2的3n+2次方，5的3n+1次方和3的3n+1次方。即：2^（3n+2）*5^（3n+1）*3^（3n+1）。

I：当n=0时可以。

II：不可以。

III：不可以。

2。（1）cow>2pig

（2）pig>12

pig+cow=2/3*60=40

if pig是13，cow至少27。13+27=40

if pig是14，cow至少29。14+29=43

所以C。

[此贴子已经被作者于2009/8/24 18:45:56编辑过]

狮子marilyn

十分感谢你！！