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歡迎您訪問數(shù)學(xué)考題練習(xí):5分和2分的硬幣共100枚,值3元2角、設(shè)5分!

數(shù)學(xué)考題練習(xí):5分和2分的硬幣共100枚,值3元2角、設(shè)5分

更新時間:2024-01-12 16:27:27作者:貝語網(wǎng)校

5分和2分的硬幣共100枚,值3元2角、設(shè)5分硬幣有a枚,2分硬幣為b枚,則2a-b的值為

A.-10

B.20

C.80

D.110

試題答案

B

試題解析

本題有兩個等量關(guān)系:5分枚數(shù)+2分枚數(shù)=100,5分總錢數(shù)+2分總錢數(shù)=320分,依此列出方程即可.

解答:根據(jù)題意得a+b=100(1);5a+2b=320(2)

第一個方程兩邊都乘3得:3a+3b=300

第二個方程減去新得到的方程得2a-b=20.

故選B.

點評:在列出方程組后不必解出就可觀察求出,進而發(fā)現(xiàn)解答問題的途徑.

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