For the school spring outing, 45% left first, and then left (1/2). There are still 40 people left. How many people from the school went to the spring outing?
学校春游，先走了45%，又走了(1/2)，还剩40人没走，学校有多少人去春游？
<gadget id="calculator">45 / 100</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (9/20) - (1/2)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">40 / (1/20)</gadget>
<output>800</output>

<result>800</result>