Known: A#B=A*B/2, then 2#(5#8)=how much.
已知：A#B=A*B/2，那么2#(5#8)=多少．
<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<result>20</result>