The school library has a total of 640 literary and technical books, of which 25% are technical books. Later, a batch of scientific and technological books were purchased, and at this time, scientific and technological books accounted for 40%. How many scientific and technological books were bought later?
学校图书馆有文艺书、科技书共640本，其中科技书占25%，后又买进一批科技书，这时科技书占40%，后又买进多少本科技书？
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(3/4) / (3/5)</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">640 * (5/4)</gadget>
<output>800</output>

<gadget id="calculator">800 - 640</gadget>
<output>160</output>

<result>160</result>