Dongfeng Primary School organized students to plant trees on the hillside. The original plan was to plant 500 trees, but it was actually completed in the morning (9/10) and the rest (1/5) in the afternoon. How many trees were actually planted less than the original plan?
东风小学组织学生到山坡植树，原计划种500棵，实际在上午完成了(9/10)，下午又完成余下的(1/5)，实际上比原计划少种了多少棵？
<gadget id="calculator">9 / 10</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">1 - (9/10)</gadget>
<output>1/10 = around 0.1</output>

<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">500 * (1/10) * (4/5)</gadget>
<output>40</output>

<result>40</result>