what does this sentence mean "it's a joke" one day evening , i was out for a shopping . one the street, i was a foreigner ,he wanted buy a caculator,but he couldn't understand what did the seller mean, so i translater for him. about how much was the caculator,and told him the seller was sold expensive,and wanted help him took discount from the seller. but he said to me " it's a joke" i thought a long time what did this sentence,but i can't understand until today can you help me ?