There are 15 tons of steel in the warehouse, 20% of the total is used for the first time, and (1/2) ton is used for the second time. How many tons are shared twice?
仓库里有15吨钢材，第一次用去总数的20%，第二次用去(1/2)吨．两次共用去多少吨？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">15 * (1/5)</gadget>
<output>3</output>

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

<gadget id="calculator">3 + (1/2)</gadget>
<output>7/2 = around 3.5</output>

<result>7/2 = around 3.5</result>