人教版七年级下册数学复习题八7、8、9、10、11题的答案(要有过程)
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人教版七年级下册数学复习题八7、8、9、10、11题的答案(要有过程)
人教版七年级下册数学复习题八7、8、9、10、11题的答案(要有过程)
人教版七年级下册数学复习题八7、8、9、10、11题的答案(要有过程)
7.
需要A型钢板x 块,需要B型钢板y块.
则 2x+y=15
X+2y=18
解得 x=4,y=7
答:需要A型钢板4块,需要B型钢板7块.
8.
设1个大桶可以盛酒X壶,1个小桶可以盛酒Y壶,列方程式:
5x+y=3 ①
x+5y=2 ②
②式两边各乘5得5x+25y=10
②-①得 24y=7
∴ y=7/24
将 y=7/24代入①得 5x+7/24=3
5x=3-7/24
5x=65/24
x=13/24
答:1个桶可以盛酒13/24壶,1个小桶可以酒7/24
9.
设弹簧原长为xcm ,进度系数为kN/m,根据题意,得:
k(16.4-x)=2 ①
k(17.9-x)=5 ②
由①式得:k=2/(16.4-x) ③
将③代入②,得:
3x=46.2
则x=15.4
答:弹簧应取15.4cm.
10.设取1角、5角、1元各X、Y、Z枚
由题意得:
X+5Y+10Z=70 ①
X+Y+Z=15 ②
消去x得 4y+9z=55.
z=(55-4y)/9=6+(1-4y)/9
y=7.
或 x=(55-9z)/4=13+(3-9z)/4
z=3.
∴x=5,y=7,z=3.
答:取1角、5角、1元各5枚、7枚、3枚 .
11.
设上坡路程为xkm,下坡路程为ykm,则平路有(3.3-x-y)km,可得方程
x/3+y/5+(3.3-x-y)/4=51/60
x/5+y/3+(3.3-x-y)/4=53.4/60
解得x=1.2 y=1.5
∴平坡路程为3.3-1.2-1.5=0.6(km)
答:从甲地到乙地时上坡,平路,下坡的路程分别是1.2km、0.6km、1.5km
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