There are 15 tons of steel in the warehouse of Uncle Wang's house. 20% of the total was used for the first time, and (1/2) of the total was used for the second time. Please help Uncle Wang calculate how many tons of steel are left?
王叔叔家的仓库里有15吨钢材．第一次用去总数的20%，第二次用去总数的(1/2)，请你帮王叔叔算一算还剩下多少吨钢材？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">1 - (1/5) - (1/2)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">15 * (3/10)</gadget>
<output>9/2 = around 4.5</output>

<result>9/2 = around 4.5</result>