Xiaohong and Xiaoming, from the school to the bookstore, it takes Xiaohong 30 minutes to walk, and Xiaoming takes 20 minutes to walk. If Xiao Ming starts again 5 minutes after Xiao Hong leaves school, how many minutes will it take to catch up with Xiao Hong?
小红和小明两人，从学校到书店，小红步行要30分钟，小明步行要20分钟．如果小红离校5分钟后，小明再出发，要走几分钟才能追上小红？
<gadget id="calculator">30 - 20</gadget>
<output>10</output>

<gadget id="calculator">5 / 10</gadget>
<output>1/2 = around 0.5</output>

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

<result>15</result>