How did Xiaoming's family cross the bridge?

Category: entertainment and leisure >> brain teaser

Problem description:

Now Xiaoming's family has crossed a bridge. It's dark when crossing the bridge, so there must be a light. Now it takes 1 second for Xiaoming to cross the bridge, 3 seconds for Xiaoming's brother, 6 seconds for Xiaoming's father, 8 seconds for Xiaoming's mother and 12 seconds for Xiaoming's grandfather. At most two people can cross the bridge at a time. The speed of crossing the bridge depends on the slowest one. The light turns on for 30 seconds and then goes out. Ask Xiaoming how to cross the bridge.

Analysis:

In the first step, Xiao Ming took his brother across the bridge, and it took Xiao Ming 4 seconds to come back. In the second step, Xiaoming crossed the river with his father and his younger brother came back, which took 9 seconds. The third step, mom and grandpa cross the river, and Xiaoming comes back, which takes 13 seconds; Finally, Xiao Ming and his brother crossed the river, which took 4 seconds, a total of 30 seconds.