Boss Zhang sells a commodity. He sold it at 80% of the price last year, and he can make a profit of 20%. Since the purchase price has increased this year, if he sells it at a 10% discount on last year’s price, the result is a 10% loss. Please help Boss Zhang did the math, how many percent has the purchase price increased this year compared to last year?
张老板出售一种商品，去年按定价的80%出售，能获利20%，由于今年买入价提高，如果按去年的定价打九折出售，结果一算，亏了10%，请你帮张老板算一算，今年买入价比去年提高了百分之几？
<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

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

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

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

<gadget id="calculator">1 * 1</gadget>
<output>1</output>

<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

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

<gadget id="calculator">1 + (1/5)</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">(4/5) / (6/5)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 * (2/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 - (2/3)</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/3) / (2/3)</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>