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第77頁(yè)

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解：設(shè)合伙人數(shù)為??$?x?$??人，羊價(jià)為??$?y?$??錢(qián)，

依題意得：

??$?5x+45=y?$??

??$?7x+3=y?$??

解得：??$?x=21，y=150?$??

答??$?：?$??合伙人數(shù)為??$?21?$??人??$?，?$??羊的價(jià)格為??$?150?$??錢(qián)。

解：設(shè)???$?1?$???本筆記本需要???$?x?$???元，???$?1?$???支水筆需要???$?y?$???元

$ 根據(jù)題意，得$

???$? {{\begin{cases} { {x+y=6}} \\{x+4y=18}\end{cases}}}?$???

解得，???$?{{\begin{cases} { {x=2}} \\{y=4}\end{cases}}}?$???

答：買(mǎi)???$?1?$???本筆記本需要???$?2?$???元，???$?1?$???支水筆需要???$?4?$???元

解：設(shè)甲種票價(jià)是??$?x?$??元，乙種票價(jià)是??$?y?$??元

?$ 根據(jù)題意，得$?

??$? {{\begin {cases} { {35x+35y=1150}} \\{35x+30y=1000}\end {cases}}}?$??

解得，??$?{{\begin {cases} { {x=\frac{20}{7}}} \\{y=30}\end {cases}}}?$??

答：甲種票價(jià)是??$?\frac{20}{7}?$?元，乙種票價(jià)是??$?30?$??元

解：設(shè)這根繩子有??????$?x?$??????m，環(huán)繞大樹(shù)一周需要繩子??????$?y?$??m

????$? 根據(jù)題意，得?$????

??????$? {{\begin{cases} { {3y=x-1.2}} \\{4y=x+0.8}\end{cases}}}?$??????

解得，??????$?{{\begin{cases} { {x=7.2}} \\{y=2}\end{cases}}}?$??????

????$? 答：這根繩子有7.2??m，環(huán)繞大樹(shù)一周需要繩子??2m.?$????

解：設(shè)??????$?1?$??????角、??????$?5?$??????角、??????$?1?$??????元的硬幣各取了??????$?x?$??????枚、??????$?y?$??????枚、??????$?z?$??????枚

根據(jù)題意，得

??????$? {{\begin{cases} { {x+y+z=15，①}} \\{0.1x+0.5y+z=7，②}\end{cases}}}?$??????

??????$? ②×10-①，?$??????得

??????$? z=\frac {55-4y}9?$??????

因?yàn)??????$?y，?$????????????$?z?$??????都為整數(shù)，則??????$?y=7，?$????????????$?z=3?$??????

把??????$?y=7，?$????????????$?z=3?$??????代入①，得??????$?x=5?$??????

所以方程組的解為??????$?{{\begin{cases} { {x=5}} \\{y=7} \\{z=3} \end{cases}}}?$??????

答：??????$?1?$??????角、??????$?5?$??????角、??????$?1?$??????元的硬幣各取了??????$?5?$??????枚、??????$?7?$??????枚、??????$?3?$??????枚

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