把文字翻译成数学符号，构建方程组模型是解此类题的关键；方案型问题就是要构建双边不等式，有几个整数解就有几种方案；某工程队现有大量的沙石需要运输．工程队下属车队有载重量为8吨、10吨的卡车共12辆，全部车辆运输一次能运输110吨沙石．

某照相机镜头焦距为10cm，小刚用它来给自己的物理小制作参展作品照相，当照相机正对作品从50cm处向22cm处移动的过程中（　　）

Trip 1  One week in the Mountains
Bring your strong shoes and warm clothes for this walk in a beautiful area of the Green Mountains. You may go hiking or have a try of rock climbing. This is also a protection area for wild animals. You can find many kinds of animals living in this area.
Time: May 8—May 14   Tel: 64639818    Adult: $110     
Trip 2  Three days in the country
There are many beautiful gardens. Take your camera and enjoy the wonderful sight in Hunter Valley. It is a good place for fishing and horse riding. Bird lovers can also enjoy a great walk.
Time: May 20—May 22        Tel: 63986423   Adult: $50      Child: $25
Trip 3  Flashlight adventure
Put on your warm clothes, bring a torch, and come for a night walk along the Dungog Valley. It's a trip full of adventure. A guide will lead the tour. Many of the plants you will see on this trip can only be seen at night.
Time: May 16—May 18     Tel: 63875629      Adult: $30       Not for children
Trip 4  Five days by the sea
Wear your sun hat and enjoy wonderful sunshine all the time from morning to evening. Our hotel is next to the sea. We have our own boats, too. You can swim in the sea or in the swimming pool. Every day our boat will take you to different places for swimming.
Time: May 23—May 27        Tel: 67538293     Adult: $80      Child: $40

 ____the doctors in their hospital is about one thousand, and sixty percent of them___________ women.