一天早晨，小明上学时先以速度v1走了路程的
，因感觉时间紧张，为避免迟到，小明紧接着以速度v2跑完剩下的路程．则小明这天在上学路上的平均速度为______．2 5
设小明上学走的总路程为s，
则走
的路程所用时间：2 5
t1=
=
s2 5 v1
，2s 5v1
走剩余
的路程所用时间：3 5
t2=
=
s3 5 v2
，3s 5v2
小明这天在上学路上的平均速度：
v=
=s总 t总
=s t1+t2
=s
+2s 5v1 3s 5v2
．5v1v2 3v1+2v2
故答案为：
．5v1v2 3v1+2v2
| 完形填空。 | |||
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| ( )1. A. look ( )2. A. her ( )3. A. than ( )4. A. what ( )5. A. early ( )6. A. under ( )7. A. soon ( )8. A. place ( )9. A. buying ( )10. A. follow | B. read B. him B. since B. why B. dear B. around B. busily B. song B. losing B. give | C. see C. other C. though C. who C. easy C. above C. hardly C. school C. sending C. make | D. watch D. others D. because D. how D.late D. between D. often D. dance D. playing D. bring |