1. "请问，您贵庚？" and "您多大年纪？ 请问，您贵庚？ sounds more formal than 您多大年纪了？Both are commonly used, depending on the occasions and the level of politeness that you would like to express. I don't know about people in China, but people in Taiwan use 你幾歲? more frequently in daily conversation. 2. 换开 and 找开 are slightly different. 换开：means you exchange the large money with others, say vendors or banks. (Ex: one 1000 bill = ten 100 bills) 找开：means you pay with a large bill and the vendor/ clerk gives you the changes (Ex: pay an item worth 100 with a 1000 bill and the other gives you back 900). 3. 大票子 and 钞票. Personally, I have never heard of 大票子 before. 钞票 is fine. If you want to say large bill, I think you can say 大鈔。 4. As for tuna sandwiches, I would say 鮪魚三明(文)治。

1.For me,use“您多大了”and"您多大年纪了" are more comfortable, and if you want to show your manner it is better to say "请问，您今年贵庚？". 2. For my opinion, “找开” means when you buy something and ask him/her if he/she have enough coins, “换开” means you ask someone to help you change your money. 3. I never say "大票子”, it is not very common. 4.金枪鱼( main land china) , 鲔鱼(Taiwan China).