A mathematical dictionary is priced at a yuan, and the profit is 20% of the cost. If the profit is increased to 30%, how much should the selling price be increased?
一本数学辞典售价a元，利润是成本的20%，如果把利润提高到30%，那么应提高售价多少元．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<result>1/12 = around 0.083333</result>