When I was young, my mother went to the market to buy fruit. She first bought 2.5kg of apples for 13.5 yuan, and then bought 5kg of bananas for 12.9 yuan. How much cheaper is the unit price of bananas than apples?
小时妈妈去市场买水果，她先花13.5元买了2.5千克苹果，又买了5千克香蕉花了12.9元，香蕉的单价比苹果便宜多少钱？
<gadget id="calculator">13.5 / 2.5</gadget>
<output>5.4</output>

<gadget id="calculator">12.9 / 5</gadget>
<output>2.58</output>

<gadget id="calculator">5.4 - 2.58</gadget>
<output>2.82</output>

<result>2.82</result>