If 100 US dollars can be exchanged for 516 francs, and 100 marks can be exchanged for 123 francs, now there are 2580 marks, how many dollars can be exchanged.
若100美元可换516法郎，又100马克可换123法郎，今有2580马克，可换多少美元．
<gadget id="calculator">2_580 / 100</gadget>
<output>129/5 = around 25.8</output>

<gadget id="calculator">123 / 516</gadget>
<output>41/172 = around 0.238372</output>

<gadget id="calculator">(129/5) * (41/172) * 100</gadget>
<output>615</output>

<result>615</result>