If you are sitting at a table with people you don't know, it is impolite to smoke without first asking if it will disturb them. At American restaurants and coffee shops, cold water is usually served before you order. You may find the bread and the butter are free, and if you order coffee, you may get a free refill.
    Most cities and towns have no rules about opening and closing time for stores and restaurants, though they usually do make rules for bars. Especially in big cities, stores may be open 24 hours a day. Serving in restaurants are often large. If you can't finish the meal but would like to enjoy the food later, ask the waiter or the waitress for a “doggie bag”(剩菜袋). It may have a picture of a dog on it, but everybody knows you are taking the food for yourself. Tips are not usually added to check. You should leave a tip of about 15% on the table when you leave. In some restaurants, a waiter or waitress often brings your check on a plate, and you can put your money there. Then the waiter or the waitress brings you your changes.

抽奖方案有以下两种，方案a：从装有2个红球、3个白球（仅颜色不同）的甲袋中随机摸出2个球，若都是红球，则获得奖金30元；否则，没有奖金，兑奖后将摸出的球放回甲袋中，方案b：从装有3个红球、2个白球（仅颜色相同）的乙袋中随机摸出2个球，若都是红球，则获得奖金15元；否则，没有奖金，兑奖后将摸出的球放回乙袋中．

抽奖条件是，顾客购买商品的金额买100元，可根据方案a抽奖一次：满150元，可根据方案b抽奖一次（例如某顾客购买商品的金额为260元，则该顾客可以根据方案a抽奖两次或方案b抽奖一次或方案a、b各抽奖一次）．已知顾客A在该商场购买商品的金额为350元．

在“比较不同物质吸热升温情况”的实验中：

一次数学课上，老师请同学们在一张长为18厘米，宽为16厘米的矩形纸板上，剪下一个腰长为10厘米的等腰三角形，且要求等腰三角形的一个顶点与矩形的一个顶点重合，其它两个顶点在矩形的边上，则剪下的等腰三角形的面积为多少平方厘米（　　）