How much is 2 pieces of 10 yuan, 4 pieces of 2 yuan, and 1 piece of 50 cents.
2张10元、4张2元、1张5角一共是多少元．
<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<gadget id="calculator">2 * 4</gadget>
<output>8</output>

<gadget id="calculator">20 + 8 + 0.5</gadget>
<output>28.5</output>

<result>28.5</result>