Taotao Math 1-Q10，31

FebWater

请教：
Q10:

A set of numbers has the property that for any number t in the set, t + 2 is in the set.If –1 is in the set, which of the following must also be in the set?



I.-3

II.1

III.5





A.I only

B.II only

C.I and II only

D.II and III only

E.I, II, and III

为什么答案选D呢，觉得是C阿


Q31:

A positive integer n is said to be “prime-saturated” if the product of all the different positive prime factors of n is less than the square root of n.What is the greatest two-digit prime-saturated integer?



A.99

B.98

C.97

D.96

E.95

这题答案是D，为什么不是C呢

gecko_liu

第一题由t in the set 可以推出t+2 in the set 但是不能由t in the set 推出 t-2 in the set
可能这个集合是从-1开始的无限集。
第二题97本身就是质数，它的质因子是1和本身 不符合条件了。

请教：
Q10:
A set of numbers has the property that for any number t in the set, t + 2 is in the set.If –1 is in the set, which of the following must also be in the set?

I.-3

II.1

III.5





A.I only

B.II only

C.I and II only

D.II and III only

E.I, II, and III

为什么答案选D呢，觉得是C阿


Q31:

A positive integer n is said to be “prime-saturated” if the product of all the different positive prime factors of n is less than the square root of n.What is the greatest two-digit prime-saturated integer?



A.99

B.98

C.97

D.96

E.95

这题答案是D，为什么不是C呢

-- by 会员 FebWater (2010/4/25 15:06:20)

FebWater

谢谢你gecko

FebWater

所以质数也是质数本身的质因数，可以这样说对吧？

gecko_liu

对啊。。。有点绕啊

FebWater

抱个，多谢