两道数学题

zhongyaya

Q27:

A pharmaceutical company received $3 million in royalties on the first $20 million in sales of the generic equivalent of one of its products and then $9 million in royalties on the next $108 million in sales.  By approximately what percent did the ratio of royalties to sales decrease from the first $20 million in sales to the next $108 million in sales?



A.    8%                                              

B.     15%C.     45%

D.    52%

E.     56%



Q29:

Is the integer n odd?

(1)     n is divisible by 3.

(2)     2n is divisible by twice as many positive integers as n
.




第一道题答案选C，第二道题答案选B,麻烦各位解答下，谢谢啦

zhongyaya

ding~

zhongyaya

再次！！！~

a10285

Q27. 第一次ratio为3/20，第二次ratio为9/108，则减少比例为（3/20-9/108）/(3/20)约等于45%，即选C

Q28. （1）显然不行，再看（2），可用正整数的因子数公式来解释，因子数公式为如正整数n可以
分解为m（x）n（y）{m、n是质因子，x、y是其幂指数}，则因子数为(x+1)(y+1)
如n是奇数，则2n可分解为m（x）n（y）2（1），则因子数为(x+1)(y+1)（1+1），翻了一番，
但如n是偶数，则不行~~

（2）正确，选B

zhongyaya

先说下：您解释的非常好~但是我还想问下  2n is divisible by twice as many positive integers as n  这句话的意思（真是怪不好意思的）


这句话的意思一开始我就没看懂，所以就蒙了
非常感谢

a10285

2n的因子数是n的因子数的2倍

zhongyaya

彻底懂了