Xiaohong read a book, read (1/5) of this book on the first day, read as much as the first day on the second day, read as much as the sum of the first two days on the third day, and read as much as the first two days on the third day. What fraction of it can be finished in four days?
小红看了一本书，第一天看了这本书的(1/5)，第二天看的和第一天同样多，第三天看的与前两天的总和同样多，第四天再几分之几可看完？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) + (1/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(1/5) + (1/5) + (2/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<result>1/5 = around 0.2</result>