15. 化简得原式=，代入得=

14. 解：(1)设乙队单独完成这项工程需要x天，则甲队单独完成这项工程需要天.

　　　 根据题意，得

　　　 解得x=90.

　　　 经检验，x=90是原方程的根.　　　　　　　　　　　　　　　　 ……3分

　　　 ∴

　　　 　答：甲、乙两队单独完成这项工程需要60天和90天.　　　　　 ……1分

　　 (2)设甲、乙两队合作完成这项工程需要y天，则有

　　　　 解得y=36.　　　　　　　　　　　　　　　　　　　　　　　 ……2分

　　　　 需要施工费用：36×(0.84+0.56)=50.4(万元).　　　　　　 ……1分

　　　　 ∵50.4＞50，

　　　　 ∴工程预算的施工费用不够用，需追加预算0.4万元.　　　　 ……1分

13. 解：原式=2x-1+　　　　　　　　　　　 ……4分

　　　　　　 =2x-1+x+2

　　　　　　 =3x+1　　　　　　　　　　　　　　　　　　　　　　 ……2分

12. 解：聪聪说的有理．······························································································· 1分

················································································ 3分

··················································································································· 4分

······························································································································· 5分

只要使原式有意义，无论取何值，原式的值都相同，为常数1．····························· 6分

11. 解：································································································ 2分

···························································································································· 5分

检验：将代入原方程，左边右边································································· 7分

所以是原方程的根································································································ 8分

(将代入最简公分母检验同样给分)

10. 解 (Ⅰ)

	速度(千米／时)	所用时间(时)	所走的路程(千米)
骑自行车			10
乘汽车			10

　　　　　　　　　　　　　　　　　　　 ···························································· 3分

(Ⅱ)根据题意，列方程得．　 ································································· 5分

解这个方程，得．　　 ······················································································· 7分

经检验，是原方程的根．

所以，．　　　　　　　　　

答：骑车同学的速度为每小时15千米． ······································································ 8分

9. 解法一：原式····························································· 2分

······················································································································· 6分

当时，原式···················································································· 8分

解法二：原式··········································· 2分

······················································································································· 6分

当时，原式···················································································· 8分

8. 解法一：设乙班有人捐款，则甲班有人捐款．············································ 1分

根据题意得：

········································································································· 5分

解这个方程得．································································································· 8分

经检验是所列方程的根．··················································································· 9分

(人)

答：甲班有48人捐款，乙班有45人捐款．································································· 10分

解法二：设甲班有人捐款，则乙班有人捐款．················································· 1分

根据题意得：

········································································································· 5分

解这个方程得．································································································· 8分

经检验是所列方程的根．··················································································· 9分

(人)

答：甲班有48人捐款，乙班有45人捐款．································································· 10分

7. 设原计划平均每天改造道路x千米，,根据题意，得…………1分

………………………………………………………4分

解这个方程，得x＝0.2………………………………………………6分

经检验，x＝0.2是原方程的解.

答:原计划平均每天改造道路0.2千米.…………………………7分四、认真思考，你一定能成

6. 解：　 　………………………………………2分

＝　　　　 …………………………………………………………3分

＝　　　　 …………………………………………………………4分

＝．　　　　 ……………………………………………………………………5分

当时，原式＝．　 ……………………………………7分