There are 400 girls in Chunlei Primary School, less than boys (1/5). How many boys are there?
春雷小学有女生400人，比男生少(1/5)，男生有多少人？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">400 / (4/5)</gadget>
<output>500</output>

<result>500</result>