It is necessary to mix 20 tons of concrete, of which stones account for 2/3 of the total, 3 tons of cement are needed, and the rest is yellow sand. How much is yellow sand in the total?
要拌制20吨混泥土，其中石子占总数的(2/3)，水泥需3吨，其余的是黄沙，黄沙占总数的多少．
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">20 * (2/3)</gadget>
<output>40/3 = around 13.333333</output>

<gadget id="calculator">20 - (40/3) - 3</gadget>
<output>11/3 = around 3.666667</output>

<gadget id="calculator">(11/3) / 20</gadget>
<output>11/60 = around 0.183333</output>

<result>11/60 = around 0.183333</result>