[原创] 十月十六日 数学机井海外版 至101

matthew8285

101. ask total distance of the round trip:

      So, it's 480 x 2 = 960

sinoversion

ding

fusiyu

这个公式不对吧。

1和200000：standard deviation is 141420.6, 但(range/2)=99999.5; 显然standard d 大。 

beyond5

以下是引用r930620在2006-10-17 20:49:00的发言：
請教一下:

270. Three quarts of chemical A contain 10% of hydrogen peroxide. A different chemical B, which contains 40% of hydrogen peroxide, will be mixed with the 3 quarts of A. How much B should be added to the A so that the resulting mixture contains 30% of hydrogen peroxide?

6

6是怎麼來的哩????

(3*10%+X*40%)=(3+x)30%

[此贴子已经被作者于2006-10-18 4:42:50编辑过]

cpcjustin

再请教一下

[sn+n(n+1)/2]/n

当中的n(n+1)/2是一个公式吗？想不起来了

1+2+3+....+n=(1+n)*(n/2) common sense.

101. A bus traveled to its destination at speed of 60km/h. On the return trip, the bus traveled the same distance, but had an average speed of 80km/h, making the trip 2 hours shorter. What is the total distance of the round trip?

480km

480*2=960km is right.  round trip

r930620

請教一下:

270. Three quarts of chemical A contain 10% of hydrogen peroxide. A different chemical B, which contains 40% of hydrogen peroxide, will be mixed with the 3 quarts of A. How much B should be added to the A so that the resulting mixture contains 30% of hydrogen peroxide?

6

6是怎麼來的哩????

joycechou

以下是引用yaomao在2006-10-16 12:49:00的发言：
大家动作的都很快的说
94题该选A吧，
standard deviation<range/2

To lz, is it a formula or definition?

Never heard this before, so thanks!!!

mc637t

95題支持A

我的方式:以A為例

設中間數為X,個差為a,則其餘各數為x-5a,x-4a,x-3a,x-2a,x-a,x,x+a,x+2a,x+3a,x+4a,

求得mean=(10x-5a)/10

新序列則為x-5a+1,x-4a+2,....,x+6,..x+4a+10,求得mean=(10X-5a+55)/10

兩者相減得55/10=5.5,故成立

以此方式B因未知總個數,故設總個數K

原序列為{kx+a*(k/2)}/K

新序列為{kx+a*(k/2)+K*(1+k)/2}/K

兩者相減得(1+k)/2,因未知K,故該數不可得,不成立

bettywushh

LS:but it asked about "how much", we need to give an number for the answer.