问题
填空题
某次比赛规定每两队之间只打一场比赛，共打了15场，则有______支球队参加比赛．
答案
设有x个球队参加比赛，
依题意得1+2+3+…+x-1=15，
即
=15，x(x-1) 2
∴x2-x-30=0，
∴x=6或x=-5（不合题意，舍去）．
答：应邀请6支球队参加比赛．
故答案为6．
搜题请搜索小程序“爱下问搜题”
某次比赛规定每两队之间只打一场比赛，共打了15场，则有______支球队参加比赛．
设有x个球队参加比赛，
依题意得1+2+3+…+x-1=15，
即
=15，x(x-1) 2
∴x2-x-30=0，
∴x=6或x=-5（不合题意，舍去）．
答：应邀请6支球队参加比赛．
故答案为6．
| Reading comprehension. (阅读短文，选择最佳答案) |
| Everybody needs water. All plants need water. We use water to wash cups, cars, clothes and ourselves. Where does all water come from? It comes from the clouds. The clouds can change into rain. Some of the rain goes down the ground. Some of the rain water goes down the mountains into streams (小溪). The streams come together to make rivers and lakes. Water can change itself. When water gets very cold, it becomes ice. When water gets very hot, it becomes steam (小蒸气). |
| 1. _____ need water. |
[ ] |
A. Only animals |
| 2. We usually clean our clothes with ______. |
[ ] |
| A. steam B. clouds C. water D. rain |
| 3. The water in the streams comes from the _____. |
[ ] |
| A. river B. lake C. wind D. clouds |
| 4. When the weather gets very , water changes into ice. |
[ ] |
| A. warm B. hot C. cool D. cold |
| 5. Where does steam come from? |
[ ] |
| A. it comes from the clouds. B. it comes from plants. C. it comes from very hot water. D. it comes from very cold water. |