Two stationery stores, A and B, sell the same pen. The original price of each pen is 10 yuan. "buy two get one free". Which store do you plan to buy if you only buy one? Why? If you are buying a lot, which store do you plan to go to? Why?
甲、乙两个文具店卖同样的一种钢笔，原定每支售价都是10元，为了吸引顾客购买，两个商店都开展了让利促销活动，甲店"打七折"，乙店"买二送一"．如果只买1支，你打算到哪个商店去购买？为什么？如果是买很多支，你打算到哪个商店去购买？为什么？
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