Xiao Ming writes homework, 30 words per minute, and can be completed in 10 minutes. If he writes 10 more words per minute, how many minutes can he finish?
小明写家庭作业，每分钟写了30个字，10分钟可以完成，如果每分钟多写10个字，几分钟可以写完？
<gadget id="calculator">30 + 10</gadget>
<output>40</output>

<gadget id="calculator">10 / 40</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">30 * (1/4)</gadget>
<output>15/2 = around 7.5</output>

<result>15/2 = around 7.5</result>