There are a total of 630 scientific and literary books in the library of the village committee of Wangjia Village, among which scientific and technological books account for 20%. Later, a batch of technical books were purchased. At this time, technical books accounted for 30% of the two books. How many technical books were purchased later?
王家村村委会图书室有科技书、文艺书共630本，其中科技书占20%．后来又买进一批科技书，这时科技书占两种书的30%，后来又买进的科技书是多少本？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<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">(4/5) / (7/10)</gadget>
<output>8/7 = around 1.142857</output>

<gadget id="calculator">630 * (8/7)</gadget>
<output>720</output>

<gadget id="calculator">720 - 630</gadget>
<output>90</output>

<result>90</result>