A printing factory originally planned to bind 180,000 exercise books in October, and completed (1/4) of the plan in the first ten days, and completed 40% of the plan in the middle and late ten days. How many thousands of copies were overfulfilled this month?
某印刷厂原计划十月份装订练习本18万本，上旬完成计划的(1/4)，中旬与下旬都完成计划的40%，这个月超额完成多少万本？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">(1/4) + (2/5) + (2/5)</gadget>
<output>21/20 = around 1.05</output>

<gadget id="calculator">18 * (21/20)</gadget>
<output>189/10 = around 18.9</output>

<gadget id="calculator">(189/10) - 18</gadget>
<output>9/10 = around 0.9</output>

<result>9/10 = around 0.9</result>