If a computer is sold at a 10% reduction in price, it can make a profit of 215 yuan; if it is sold at a 20% reduction in price, it will lose 215 yuan. How much is the purchase price of this computer?
一台电脑，如果减少定价的10%出售，可盈利215元；如果减少定价的20%出售，就亏本215元．这种电脑的进价是多少元？
<gadget id="calculator">215 + 215</gadget>
<output>430</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/5) - (1/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">430 / (1/10)</gadget>
<output>4_300</output>

<gadget id="calculator">1 - (1/10)</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">4_300 * (9/10)</gadget>
<output>3_870</output>

<gadget id="calculator">3_870 - 215</gadget>
<output>3_655</output>

<result>3_655</result>