A bookstore shipped a batch of science and technology books for teenagers. They sold (3/10) on the first day, sold (1/5) more than the first day on the second day, and sold 30 more books on the second day. How many books of this kind are there for teenagers?
某书店运来一批少年科技书，第一天卖了(3/10)，第二天比第一天多卖了(1/5)，第二天多卖了30本，书店运来的这种少年科技书一共有多少本？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">30 / (1/5) / (3/10)</gadget>
<output>500</output>

<result>500</result>