OG里的几个数学题死活不理解，求解啊！！！

考啥都过 · 发表于 2018-2-19 00:25:51

楼主数学渣，cder都说数学容易到略过我却还有好多不懂......哭泣

我把几个我不懂的贴上来，求大神解释啊啊啊啊（因为不止一个题，我就分楼发，随便帮解哪个都行，蟹蟹！）

List T consists of 30 positive decimals, none of which is an integer, and the sum of the 30 decimals is S. The estimated sum of the 30 decimals, £, is defined as follows. Each decimal in T whose tenths digit is even is rounded up to the nearest integer, and each decimal in T whose tenths digit is odd is rounded down to the nearest integer; E is the sum of the resulting integers. If
13 of the decimals in T have a tenths digit that is even, which of the following is a possible value of E - S ?

I.-16

II.6

III.10

AI only
BI and II only
CI and III only
DII and III only
EI,II, and III

考啥都过 · 发表于 2018-2-19 00:35:01

For the past n days, the average (arithmetic mean) daily production at a company was 50 units. If today's production of 90 units raises the average to 55 units per day, what is the value of n ?
A30
B18
C10
D9
E7

这个题说的90是原本生产50个，因为生产了90个所以把平均生产个数拉到55的意思吗如果是那为啥不是用多生产的45除5，OG解析里的90不太懂。。。。

考啥都过 · 发表于 2018-2-19 00:35:57

Last year the price per share of Stock X increased by k percent and the earnings per share of Stock X increased by m percent, where k is greater than m. By what percent did the ratio of price per share to earnings per share increase, in terms of k and m?
Akm%
B(k-m) %
C100(k−m)100+k%
D100(k−m)100+m%
E100(k−m)100+k+m%

考啥都过 · 发表于 2018-2-19 00:37:43

Seven pieces of rope have an average (arithmetic mean) length of 68 centimeters and a median length of 84 centimeters. If the length of the longest piece of rope is 14 centimeters more than 4 times the length of the shortest piece of rope, what is the maximum possible length, in centimeters, of the longest piece of rope?
A82
B118
C120
D134
E152

这个题OG解释说要使得最大的14+4a成立，就要让中位数前的三个数等于a，中位数后的两个等于中位数，为啥？？？

考啥都过 · 发表于 2018-2-19 00:38:56

In a box of 12 pens, a total of 3 are defective. If a customer buys 2 pens selected at random from the box, what is the probability that neither pen will be defective?
A16
B29
C611
D916
E34

sweetbabyff · 发表于 2018-2-22 10:42:02

E-S（max)=-0.02*13+0.99*17=17-0.43=16.57
E-S(min)=-0.98*13+0.01*17=-13+0.43=-12.57
因为6，10落在16.57和-12.57之间，所以我认为选d

sweetbabyff · 发表于 2018-2-22 10:45:55

考啥都过发表于 2018-2-19 00:35
For the past n days, the average (arithmetic mean) daily production at a company was 50 units. If to ...

(90+n*50)/(n+1)=55
n=7

sweetbabyff · 发表于 2018-2-22 11:13:21

[quote][/quote]
[img]第三题

sweetbabyff · 发表于 2018-2-22 15:30:50

考啥都过发表于 2018-2-19 00:38
In a box of 12 pens, a total of 3 are defective. If a customer buys 2 pens selected at random from t ...

AMBER513 · 发表于 2019-8-22 08:15:22

看一下！

[考古] OG里的几个数学题死活不理解，求解啊！！！

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