The school used 3.02 tons of coal the year before last, and last year it used 0.5 tons less than the year before. How many tons of coal was used last year?
学校前年用煤3.02吨，去年比前年少用0.5吨，去年用煤多少吨？
<gadget id="calculator">3.02 - 0.5</gadget>
<output>2.52</output>

<result>2.52</result>