There are 500 storybooks in the library, 30% of which are lent out and 30% are returned, how many storybooks are there in the library now?
图书馆有500本故事书，借出了30%后，又归还了30%，图书馆现在有故事书多少本．
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (3/10)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">1 + (3/10)</gadget>
<output>13/10 = around 1.3</output>

<gadget id="calculator">500 * (7/10) * (13/10)</gadget>
<output>455</output>

<result>455</result>