A copy of "Mathematical Stories" is 31 yuan. If 1 US dollar is exchanged for 6.2 yuan, how many dollars are needed to buy this book.
一本《数学故事》31元人民币，如果1美元兑换6.2元人民币，买这本书需要多少美元．
<gadget id="calculator">31 / 6.2</gadget>
<output>5</output>

<result>5</result>