求助数学

水享

请XDJM解释详细点，多谢了

If n is the product of the integers from1 to 20 inclusive, what is the greatest integer k for which 2k is a factor of n?

A.    10
B.    12
C.    15
D.    18
E.    20


In a corporation, 50 percent of the male employees and 40 percent of the female employees are at least 35 years old.  If 42 percent of all the employees are at least 35 years old, what fraction of the employees in the corporation are females?

A.    3/5
B.    2/3
C.    3/4
D.    4/5
E.    5/6


If 1050 – 74 is written as an integer in base 10 notation, what is the sum of the digits in that integer?

A.    424
B.    433
C.    440
D.    449
E.    467

LJWISC1OL

1) 我觉得怎么这题那么怪。。。答案是20么？如果是的话。。。用代入法，求答案

2)In a corporation, 50 percent of the male employees and 40 percent of the female employees are at least 35 years old.  If 42 percent of all the employees are at least 35 years old, what fraction of the employees in the corporation are females?

male:M          
female:F
0.5M+0.4F=0.42(M+F)===  0.5(M/F)+0.4=0.42((M/F)+1)===M/F=1/4
ask: F/(M+F)=4/(1+4)=4/5==D


3)If 1050 – 74 is written as an integer in base 10 notation, what is the sum of the digits in that integer?

哥们，这是10的50次方吧
10^50-74
1000-74=926
10000-74=9926
~~类推，3个0就1个9,4个0就2个9。。。。50个0就48个9
所以48*9+2+6=440

卖报的小行家

第一题: 2的K次方 不是2k. 答案是K=18. 2的K次方乘以a来表示N的因子，如果要这个因子最大，就是N本身。N本身就是N的因子。 把1到20的乘积的2的个数找出来就知道了。