Li Ying reads a technical book for 3 days, and there are 120 pages left. If she reads it at this speed for 3 days, only 2/5 of the whole book is left. How many pages does this book have?
李颖看一本科技书，看了3天，剩下120页，如果用这样的速度看3天，就剩下全书的(2/5)．这本书一共有多少页？
<gadget id="calculator">3 + 3</gadget>
<output>6</output>

<gadget id="calculator">2 / 5</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">6 / (3/5)</gadget>
<output>10</output>

<gadget id="calculator">10 - 3</gadget>
<output>7</output>

<gadget id="calculator">7 / 10</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">140 / (7/10)</gadget>
<output>200</output>

<result>200</result>