A certain refrigerator factory planned to produce 4,000 refrigerators last year, but actually produced 4,500 refrigerators. What percentage was the increase in production?
某电冰箱厂去年计划生产电冰箱4000台，实际生产了4500台，增产了百分之几？
<gadget id="calculator">4_500 - 4_000</gadget>
<output>500</output>

<gadget id="calculator">500 / 4_000</gadget>
<output>1/8 = around 0.125</output>

<result>1/8 = around 0.125</result>