Four people need to cross a dark, fragile bridge at night with one flashlight. The bridge holds at most two people at a time, moving at the speed of the slower person, and someone must return the flashlight. Person A takes 1 minute, B takes 2 minutes, C takes 5 minutes, and D takes 10 minutes. What is the fastest total time to get everyone across?
17 minutes
A and B cross first (2 min). A returns with flashlight (1 min, total 3). C and D cross together (10 min, total 13). B returns with flashlight (2 min, total 15). A and B cross together again (2 min, total 17).
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Medium. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
More logic riddles
Two mothers and two daughters went shopping together. They bought exactly three identical umbrellas, and each person walked home with her own umbrella. How is this possible without anyone sharing?
In a race of five runners, Leo finished ahead of Max. Nora finished behind Owen. Paul finished right between Leo and Max. Owen finished ahead of Leo. What is the exact finishing order from first to last?
In a drawer, there are 10 matching black socks, 10 matching white socks, and 10 matching red socks. The room is pitch black. What is the minimum number of socks you must pull out to guarantee you have at least one complete matching pair of any color?
If 1 = 3, 2 = 3, 3 = 5, 4 = 4, 5 = 4, and 6 = 3, what does 7 equal according to this pattern?
Three runners—Xander, Yuri, and Zane—compete in a sprint. Xander finished before Yuri. Yuri finished immediately before Zane. Zane did not finish last. Is this outcome possible?
A shepherd needs to cross a river with a wolf, a goat, and a cabbage. His boat can carry only himself and one item at a time. If left unattended, the wolf will eat the goat, and the goat will eat the cabbage. How many one-way river crossings must the shepherd make to transport all three safely to the other side?