Mom bought a book of 27.6 yuan and a book of 15.9 yuan, and paid 50 yuan. How much should I get back?
妈妈买了一本27.6元和一本15.9元的书，付出50元．应找回多少元？
<gadget id="calculator">27.6 + 15.9</gadget>
<output>43.5</output>

<gadget id="calculator">50 - 43.5</gadget>
<output>6.5</output>

<result>6.5</result>