pile of apples, A took away 20% of the whole, B took away 30% of the whole, C took away 50% of the sum of the apples taken by A and B, and there are still 10 apples left, this pile of apples How many are there?
一堆苹果，甲取走了全部的20%，乙取走了全部的30%，丙取走了甲、乙两人取走苹果之和的50%，这时还剩10个，这堆苹果原有多少个？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">(1/5) + (3/10)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

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

<gadget id="calculator">1 - (1/5) - (3/10) - (1/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">10 / (1/4)</gadget>
<output>40</output>

<result>40</result>