16)Ａ完成Ｗ工作比B完成此工作多用2天，A&B共同完成(5/4)*W需用3天，问A完成2W需用几天？
ANS:12天
[确认]12天
[思路]set A complete x of W job per day , B ,y
the equation will be
W/x=W/y+2 , (5/4)W/(x+y)=3
x=1/6W
2/(1/6)=12
The answer does not make sense to me. Why the equation has to be W/x=W/y+2 , (5/4)W/(x+y)=3
x=1/6W
2/(1/6)=12
There are three unknow, but how you got x= 1/6W. Why (5/4)W/(x+y) = 3?
14)During a trans-atlantic trip ticket, 20% held round-trip and with cars aboard, 60% held round trip ticket with no car aboard. ask the total percentage of persons held round-trip ticket.
30%, 60%, 66-1/3 %
hope somebody help me. No answer is bigger than 66.3333%
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[思路]no idea...
[08]
我算的是50%， 不知道对不对
我是这样算的：
60%的人有R but no C , 所以有40% 的人有R&C, 设有R的人数为X
40%X = 20% X=50%
to littlegal
5 购人排名, A 总在B之前的total
30; 60; 80;120
Answer: 60
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P5 is all the possible situation of different orders
divide by 2 is because , of all the situations
one case is that A is in front of B while another is that B is in front of A
16)Ａ完成Ｗ工作比B完成此工作多用2天，A&B共同完成(5/4)*W需用3天，问A完成2W需用几天？
ANS:12天
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to simplify this problem , you may forget the W
set A complete a of the total job per day, to finish the whole , he needs 1/a days
set B complete b of the total job per day ,to finish the whole , he needs 1/b days
Ａ完成Ｗ工作比B完成此工作多用2天 then 1/a=1/b+2
A&B共同完成(5/4)*W需用3天 then (5/4)/(a+b)=3
only two unknown numbers with two equations , you get the ans ^^
to qqks
I think it makes sense !
and you remind me another problem :
An insurance company has a paper record and an electronic record for every claim. For an inaccurate paper record, 60% chances that the electronic record is inaccurate. For an inaccurate electronic record, 75% chances that the paper record is inaccurate. 3% of all the claims are inaccurate both in paper record and in electronic record. Pick one claim randomly, what are the chances that it is both accurate in paper record and in electronic record?
A.97% B.94% C.68% D.65% E.35%
【确定】B 94%,
For an inaccurate paper record, 60% chances that the electronic record is inaccurate.
x * 60% = 3% x = 5% (inaccurate paper record)
For an inaccurate electronic record, 75% chances that the paper record is inaccurate.
y * 75% = 3% y = 4% (inaccurate electronic record)
=> 2% inaccurate paper record, accurate electronic record
=> 1% inaccurate electronic record, accurate paper record
inaccurate paper record + inaccurate electronic record = 6%
ans:94%
14)During a trans-atlantic trip ticket, 20% held round-trip and with cars aboard, 60% held round trip ticket with no car aboard. ask the total percentage of persons held round-trip ticket.
30%, 60%, 66-1/3 %
hope somebody help me. No answer is bigger than 66.3333%
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[思路]no idea...
[08]
