题目

House Sitting In many countries of the world people do what is called house sitting. It means that if owners of the house are going away, they want someone to come into their home and look after the house and maybe pets while they are away. In Australia, many people travel. After people retire, they might buy a van and travel all over the country. 36． So if someone wants to travel or go away for some reason, they might want someone in their home to care for it and keep the gardens tidy. House sitters might have to care for pets. Also, quite a few people have swimming pools in their ba某校一间宿舍里住有若干位学生，其中一人担任舍长．元旦时，该宿舍里的每位学生互赠一张贺卡，并且每人又赠给宿舍楼的每位管理员一张贺卡，每位宿舍管理员也回赠舍长一张贺卡，这样共用去了51张贺卡．问这间宿舍里住有多少位学生．