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2011中考模拟分类汇编8.二元一次方程(组)

2011中考模拟分类汇编8.二元一次方程(组)
2011中考模拟分类汇编8.二元一次方程(组)

二元一次方程(组)

一、选择题

1.(2011年浙江省杭州市城南初级中学中考数学模拟试题)若1++y x 与()2

2--y x 互为相

反数,则3)3(y x -的值为 ( ) A.1 B.9 C.–9 D.27 答案:D

2、(2011湖北省崇阳县城关中学模拟)已知()0332

=++++m y x x 中,y 为负数,则m

的取值范围是( )

A. m >9

B. m <9

C. m >-9

D. m <-9 答案:A

3、(2011年海宁市盐官片一模)解方程组23739x y x y +=??

+=? ,①-②得( )

A .32x = B. 32x =- C. 2x = D. 2x =- 答案:D

二、填空题

1、(2011年北京四中五模)方程组???=-=+5

6

xy y x 的解是 .

答案:?

?

???

?5y 1x 1y 5x =-=-=-=- 2.(淮安市启明外国语学校2010-2011学年度第二学期初三数学期中试卷)已知x ,y 满足

方程组23,37.x y x y -=??+=?①②

求x +2y 的值为 .

答案:4

3、 (2011深圳市模四)若关于x ,y 的二元一次方程组?

??=-=+k y x ,

k y x 95的解也是二元一次方程

632=+y x 的解,则k 的值为_______。

答案:

4

3

三、解答题

1、(中江县2011年初中毕业生诊断考试)

新年新举措——我县某工艺品销售公司今年一月份调整了职工的月工资分配方案,调整后月 工资由基本保障工资和计件奖励工资两部分组成(计件奖励工资=销售每件的奖励金额×销

售的件数). 下表是甲、乙两位职工今年2月份的工资情况信息: (1)试求工资分配方案调整后职工的月基本保障

工资和销售每件产品的奖励金额各是多少? (2)若职工丙今年三月份的工资不低于3000元,

那么丙该月至少应销售多少件产品?

答案:解:(1)设调整后职工的月基本保障工资为x 元,销售每件产品的奖励金额为y 元,

根据题意得方程: ?

?

?=+=+.2500300,2000200y x y x

解这个方程组得:???==.

5,1000

y x

故调整后职工的基本保障工资为每月1000元,销售每件产品的奖励金额是5元. (2)设职工丙该月至少应销售z 件产品,则1000+5z ≥3000, 解之得:z ≥400.

即职工丙该月至少应销售400件产品.

2、(2011重庆市纂江县赶水镇)解方程组 355223x y x y -=??+=?,

答案:解: ①×2+②得,11x=33. 解得,x=3. 把x=3代入①得y=4. ∴??

?==4

y ,

3x 是原方程的解.

3、(重庆一中初2011级10—11学年度下期3月月考)

解方程组?

?

?=-=+128

53y x y x

答案:.解方程组???=-=+12853y x y x

解:由②得y=2x -3代入①得:

3x+5(2x -1)=8 3x+10x -5=8 13x=13 X=1 代入③得

y=2×1-1=1

∴原方程的解为?

?

?==11y x

职工 甲 乙 月销售件数(件) 200 300 月工资(元)

2000

2500

① ②

4、(2011年北京四中三模) 国庆节,甲、乙两班学生到集市上购买苹果,,苹果的价格如下:

甲班分两次共购买苹果70千克(第二次多于第一次),共付出189元,而乙班则一次购买苹果70千克。

(1)乙班比甲班少付多少元?

(2)甲班第一次、第二次分别购买苹果多少千克?

答案:(1)49元 (2)28、42 5、(2011年江苏盐都中考模拟)某汽车制造厂开发了一款新式电动汽车,计划一年生产安装240辆.由于抽调不出足够的熟练工来完成新式电动汽车的安装,工厂决定招聘一些新工人;他们经过培训后上岗,也能独立进行电动汽车的安装.生产开始后,调研部门发现:1名熟练工和2名新工人每月可安装8辆电动汽车;2名熟练工和3名新工人每月可安装14辆电动汽车.

(1)每名熟练工和新工人每月分别可以安装多少辆电动汽车?

(2)如果工厂招聘n (0

成一年的安装任务,那么工厂有哪几种新工人的招聘方案?

(3)在(2)的条件下,工厂给安装电动汽车的每名熟练工每月发2000元的工资,给每

名新工人每月发1200元的工资,那么工厂应招聘多少名新工人,使新工人的数量

多于熟练工,同时工厂每月支出的工资总额W (元)尽可能的少?

解:(1)设每名熟练工和新工人每月分别可以安装x,y 辆电动汽车.

28

2314x y x y +=??

+=? 解之得

42x y =??

=?

每名熟练工和新工人每月分别可以安装4辆、2辆电动汽车.(3分) (2)设需熟练工m 名,依题意有:2 n ×12+4m ×12=240, n =10-2m

∵0

∴18m n =??

=? 26m n =??=? 34m n =??=? 4

2m n =??=?

(3分) (3)依题意有:W=1200n+(5-12n )×2000=200 n+10000,要使新工人数量多于熟练工,

满足n=4、6、8,故当n=4时,W 有最小值=10800元(4分

6、(2011年北京四中中考模拟18)某商场按定价销售某种电器时,每台可获利48元;按定价的九折销售该电器6台与将定价降低30元销售该电器9台所获得的利润相等,该电器每台的进价、定价各是多少元?

解:设该电器每台的进价为x 元,定价为y 元。

购苹果数 不超过30千克 30千克以上但不超过50千克 50千克以上 每千克价格 3元 2.5元 2元

)(小时x

)(吨y

O

8 2 4 10

3

A

B

C

)(小时x

)(吨y

O

8 2 4 10

3

A

B

C

依题意得???--=-=-)30(9)9.0(648x y x y x y 解得?

??==210162

y x

答:该电器每台的进价、定价各是162元、210元。

7、萧山新星塑料厂有甲、乙、丙三辆运货车,每辆车只负责进货或出货,丙车每小时的运输量最多,乙车每小时的运输量最少,乙车每小时运6吨,下图是甲、乙、丙三辆运输车开始工作后,仓库的库存量y (吨)与工作时间x (小时)之间的函数图像,其中OA 段只有甲、丙两车参与运输,AB 段只有乙、丙两车参与运输,BC 段只有甲、乙两车参与运输。 (1)甲、乙、丙三辆车中,谁是进货车? (2)甲车和丙车每小时各运输多少吨?

(3)由于仓库接到临时通知,要求三车在8小时后同时开始工作,但丙车在运送

10吨货物后出现故障而退出,问:8小时后,甲、乙两车又工作了几小时,使仓库的库存量为6吨?

(1)乙、丙是进货车,甲是出货车。……………………………………3分 (2)设:甲、丙两车每小时运货x 吨和y 吨,

则 ()()()?

??==???-=-++=-108

41065642y x :x y x y 解得

∴甲车和丙车每小时各运8吨和10吨。…………………………………7分 (3)设:经过m 小时后,库存是6吨,

则m(6-8)+10=-4,解得:m=7…………………………………………………9分 答:甲、乙两车又工作了7小时,库存是6吨。…………………………10分

8、 (2011杭州上城区一模) 由于电力紧张,某地决定对工厂实行“峰谷”用电.规定:在每天的8:00至22:00为“峰电”期,电价为a 元/度;每天22:00至8:00为为“谷电”期,电价为b 元/度.下表为某厂4、5月份的用电量和电费的情况统计表:

月份 用电量(万度)

电费(万元)

4 12 6.4 5

16

8.8

(1)若4月份“谷电”的用电量占当月总电量的

1

3

,5月份“谷电”的用电量占当月总用电量的

4

1

,求a 、b 的值. (2)若6月份该厂预计用电20万度,为将电费控制在10万元至10.6万元之间(不含10万

元和10.6万元),那么该厂6月份在“谷电”的用电量占当月用电量的比例应在什么范围?

答案:(1) 由题意,得

32×12a +31

×12b=6.4 8a +4b =6.4 43×16a+4

1

×16b=8.8 12a +4b =8.8 解得 a =0.6 b =0.4

(2)设6月份“谷电”的用电量占当月总电量的比例为k . 由题意,得10<20(1-k)×0.6+20k×0.4<10.6 解得0.35<k <0.5

答:该厂6月份在平稳期的用电量占当月用电量的比例在35%到50%之间(不含35%和50%).

9、(北京四中2011中考模拟12)“五一”期间,某商场搞优惠促销,决定由顾客抽奖确定

折扣.某顾客购买甲、乙两种商品,分别抽到七折(按售价的70%销售)和九折(按售价的90%销售),共付款386元,这两种商品原销售价之和为500元.问:这两种商品的原销售价分别为多少元?

答案:解:设甲、乙两种商品的原销售价分别为x ,y 元,根据题意,得:

??

?=+=+3869.07.0500y x y x ,解得:?

??==180320

y x 答:甲、乙两种商品的原销售价分别为320元,180元。

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