library has a total of 630 scientific and literary books, among which scientific books account for (1/5). Later, some scientific books were bought, and at this time, scientific books accounted for (3/10) of the total. How many technical books did you buy?
某图书馆有科技书和文艺书共630本，其中科技书占(1/5)，后来又买来一部分科技书，这时科技书占总数的(3/10)．又买来科技书多少本？
<gadget id="calculator">1 / 5</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">3 / 10</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>