The school holds a composition competition with first, second and third prizes. The first and second prizes account for 2/5 of the winners, the second and third prizes account for 9/10 of the winners, and the second and third prizes account for 9/10 of the winners. What percentage of the number of winners are those who are waiting for the prize?
学校举行作文竞赛，设一、二、三等奖，获一、二等奖的占获奖人数的(2/5)，获二、三等奖的占获奖人数的(9/10)，获二等奖的占获奖人数的几分之几？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">9 / 10</gadget>
<output>9/10 = around 0.9</output>

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

<gadget id="calculator">(2/5) + (-1/10)</gadget>
<output>3/10 = around 0.3</output>

<result>3/10 = around 0.3</result>