Xiao Qiang, Xiao Ming, Xiao Hong and Xiao Rong came home from an outing when it was getting late. They came to the east bank of a river and wanted to cross a wooden bridge to reach the west bank, but they only had a flashlight in their hands. Small, only 2 people can pass each time, so 2 people must first cross the bridge with a flashlight, and 1 person will send the flashlight back, and then 2 people will cross the bridge with the flashlight...until 4 people pass the small wooden bridge. Known: It takes 1 minute for Xiaoqiang to cross the bridge alone; 1.5 minutes for Xiaoming to cross the bridge alone;
小强、小明、小红和小荣4个小朋友郊游回家时天色已晚，他们来到一条河的东岸，要通过一座木桥到达西岸，但是他们手中只有一盏手电，由于桥的承重量小，每次只能通过2人，因此必须先由2个人拿手电过桥，并由1个人再将手电筒送回，再由2个人拿着手电筒过桥…直到4个人都通过小木桥．已知：小强单独过桥要1分钟；小明单独过桥要1.5分钟；小红单独过过桥要2.5分钟；那么4个人都通过小木桥共需要多少分钟．
<gadget id="calculator">1.5 + 1.5 + 2.5 + 1 + 1.5</gadget>
<output>8</output>

<result>8</result>