The profit of a certain learning machine is 30% of the purchase price. It is known that its retail price is 780 yuan each. How much is the purchase price of this learning machine?
某种学习机的利润是进价的三成，已知它的零售价是每台780元．这台学习机的进价是每台多少元？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 + (3/10)</gadget>
<output>13/10 = around 1.3</output>

<gadget id="calculator">780 / (13/10)</gadget>
<output>600</output>

<result>600</result>