Xiao Ming just bought 35 stamps of 20 cents and 50 cents with 10 yuan. How many stamps of 20 cents did he buy?
小明用10元钱正好买了20分和50分的邮票共35张，20分邮票买了多少张．
<gadget id="calculator">0.5 * 35</gadget>
<output>17.5</output>

<gadget id="calculator">17.5 - 10</gadget>
<output>7.5</output>

<gadget id="calculator">0.5 - 0.2</gadget>
<output>0.3</output>

<gadget id="calculator">7.5 / 0.3</gadget>
<output>25</output>

<result>25</result>