The cafeteria brings (7/8) tons of coal, (1/4) of this pile of coal is used on the first day, (1/2) of this pile of coal is used on the second day, how much of this pile of coal is left Useless.
食堂运来(7/8)吨煤，第一天用去了这堆煤的(1/4)，第二天用去了这堆煤的(1/2)，还剩这堆煤的多少没有用．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">1 - (1/4) - (1/2)</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>