Xiao Ming and his mother go to the supermarket to buy bananas, 5 yuan per kilogram of bananas. Mom bought 2.9 kilograms and paid 15 yuan. How much should I get back?
小明和妈妈去超市买香蕉，每千克香蕉5元，妈妈买了2.9千克，付出15元，应找回多少钱？
<gadget id="calculator">2.9 * 5</gadget>
<output>14.5</output>

<gadget id="calculator">15 - 14.5</gadget>
<output>0.5</output>

<result>0.5</result>