[求助]9号要考试,请求帮助几条数学题

一瞥

1. In each  production lot for a certain toy, 25 percent of the toys are red and 75 percent of the toys are blue. Half the toys are sizeA and half are size B. If 10 out of a log of 100 toys are red and size A, how many of the toys are blue and size B?

(a)15   (b) 25   (c)30  (d)35  (e)40

2.An instructor scored a student's test of 50 questions by subtacting 2 times the number of incorrect answers. If the student answerd all of the questions and received a score of 38, how many questions did that student answer correctly?

(a)19  (b) 38  (c)41  (d)44  (e)46

3.A student responded to all of the 22 questions on a test and received a score of 63.5. If the scores were derived by adding 3.5 points for each correct answer and deduction 1 point for each incorrect answer, how many questions did the student answer incorrectly?

(a)3 (b) 4  (c)15  (d)18  (e)20

4. One-fifth of the lights switches produced by a certain factory are defective. Four-fifths of the defectives switches are rejected and 1/20 of the nondefective switches are rejected by mistake. If all the switches not rejected are sold, what percent of the switches sold by the factory are defective?

(a)4% (b) 5%(c)6.25% (d)11% (e)16%

一瞥

能否有人回答下我的问题??

 

jerryszh

2题3题 列二元一次方程就可以求得答案：

2. x+y=50 x-2y=38 3.x+y=22 3.5x-y=63.5, 设x,y分别是做对的题个数，和做错题的个数

4.Sold Switches=1-(1/5*4/5+4/5*1/20)=4/5, Defective Sold: 1/5*1/5=1/25, Defective sold/sold =(1/25)/(4/5)=1/20

kevinling

LS答了2，3，4

我说说第1题吧:

100个toy(25 RED,75BLUE或者50 SizeA,50SizeB)，10个Red&A

则BLUE&A=50-10=40,那么BLUE&B=75-BLUE&A=35

[此贴子已经被作者于2008-5-8 22:02:05编辑过]

一瞥

4.Sold Switches=1-(1/5*4/5+4/5*1/20)=4/5, Defective Sold: 1/5*1/5=1/25, Defective sold/sold =(1/25)/(4/5)=1/20

为什么Defective Sold: 1/5*1/5=1/25,这个不是很懂??

原来另外几题这么简单,看来我真的想太复杂拉