问题 解答题

李明从厦门乘汽车沿高速公路前往A地,已知该汽车的平均速度是100千米/小时,它行驶t小时后距厦门的路程为s1千米;王红从A地乘汽车沿同一条高速公路回厦门,已知这辆汽车距厦门的路程s2(千米)与行驶时间t(小时)之间的函数关系式为

s2=720-80t.若两车同时出发,问:

(1)出发多少小时后两车相遇;

(2)在两车相遇之前,两车相距的路程小于288千米,求t的取值范围.

答案

(1)当两车相遇时,s1=s2

即100t=-80t+720,

解得t=4,

答:出发4小时后两车相遇;

(2)∵当两车相遇时,s1=s2

∴当两车相距288公里时,s2-s1=288,

由题意得此时s1<s2 s2-s1<288,

100t<-80t+720
-80t+720-100t<288

解得

t<4
t>2.4

∴t的取值范围是:2.4<t<4.

阅读理解
请阅读下 * * 位志愿者的简历,完成任务。
(A)根据所提供的信息,将志愿者的姓名填入相应的空白处,并阐明选择该工作的原因,同时选择符合句子的代词。
1. 例:Jennifer can help to fix up the machines in a poor elementary school because she (he, she) likes fixing
          up things.
2. ________ can help work in an animal hospital because ________ (he, she) likes ______.
3. ______ can sing and dance to cheer up the old people because _________(he, she) likes ________.
4. _______ can help the kids at local elementary schools to finish their schoolwork on Sunday because             
  (he, she) likes ________.
(B)请阅读Jennifer的来信,仿照下面的范文替John或Mary写一封自荐信。
Dear Mr. Black,
        I'm Jennifer, a 16-year-old girl. I want to be a volunteer. I like fixing up things, so I can help fix up
toys for kids in an elementary school.
                                                                                                                                         Jennifer
Dear Mr. Black. 
                                                                                                                                                     
                                                                                                                                                     

                                                                                                                                                     
判断题