Imagine a wildfire is spreading quickly through the grasslands. Three lions and three wildebeest need to escape to safety by crossing a river filled with crocodiles. Luckily, there’s a raft nearby that can carry two animals at a time. But there’s a catch: if the lions ever outnumber the wildebeest on either side of the river, the wildebeest could be in danger.
To solve this puzzle, you need to think about each move carefully. There are different ways to start the crossing:
If one animal goes alone, it must return with the raft. If two wildebeest go first, the one left behind will be in danger. Sending two lions or one of each animal can work, but let’s focus on sending one lion and one wildebeest first.
Let’s say one lion and one wildebeest cross the river. If the lion stays and the wildebeest returns, the remaining wildebeest will be safe. Now, you have the same choices again, but with one lion already on the other side.
If two wildebeest go next, one will be left behind and in danger. If one of each animal goes, the wildebeest on the raft will be outnumbered when it reaches the other side. So, at the third crossing, only the two lions can go. One lion stays, and the other returns with the raft.
Now, two wildebeest can cross safely. If two lions go back, they would outnumber the wildebeest on the other side. So, one lion and one wildebeest return, leaving one of each animal on one side and two of each on the other.
Next, the two wildebeest cross again. Now, all the wildebeest are safe on the other side. The last step is for the remaining lion to return and bring the other lions over one by one.
In total, it takes eleven trips to get everyone across the river safely. The lions and wildebeest escape the fire just in time and start their new lives on the other side. Who knows how long their unusual friendship will last now that the danger is gone?
Using craft materials like paper, cardboard, and small animal figures or drawings, create a model of the river crossing scenario. Arrange the animals and raft to visualize the puzzle. Try to solve the riddle by physically moving the pieces, ensuring the lions never outnumber the wildebeest on either side. This hands-on activity will help you understand the problem better.
Imagine a different scenario where other animals or characters need to cross a river with similar rules. Write a short story describing their journey and how they solve the puzzle. Share your story with the class and discuss the strategies used. This will help you think creatively and apply the concepts to new situations.
Create a simple board game based on the river crossing riddle. Use a grid to represent the river and design cards or dice to determine moves. Play the game with classmates, taking turns to solve the puzzle. This activity will make learning fun and encourage strategic thinking.
Work in pairs to solve a series of math and logic puzzles related to the river crossing. Each puzzle should involve similar constraints, such as ensuring balance between groups. Discuss your solutions and strategies with your partner to improve your problem-solving skills.
Use a simple animation tool or app to create a digital story of the river crossing riddle. Animate the animals’ journey across the river, showing each step of the solution. Share your animation with the class to demonstrate your understanding of the puzzle and your creativity.
As a wildfire rages through the grasslands, three lions and three wildebeest flee for their lives. To escape the fire, they must cross a crocodile-infested river. Fortunately, there is a raft nearby that can carry up to two animals at a time and requires at least one animal on board to row it across. However, if the lions ever outnumber the wildebeest on either side of the river, there could be serious consequences.
What’s the fastest way for all six animals to get across without any issues?
If you’re trying to solve this, consider listing all the decisions you can make at each point and the consequences of each choice. For instance, there are five options for who goes across first: one wildebeest, one lion, two wildebeest, two lions, or one of each. If one animal goes alone, it will have to return. If two wildebeest cross first, the remaining one will be left vulnerable.
Sending two lions or one of each animal can both lead to solutions in the same number of moves. For the sake of time, let’s focus on sending one of each animal across first. If the wildebeest stays and the lion returns, there will be three lions on one side, which is not safe for the remaining wildebeest.
So, we need to have the lion stay on one side while the wildebeest returns. Now we have the same five options, but with one lion already on one side. If two wildebeest go, one will be left behind and in danger. If one of each animal goes, the wildebeest on the raft will be outnumbered as soon as it reaches the other side.
This means that at the third crossing, only the two lions can go. One gets dropped off, leaving two lions on one side. The third lion takes the raft back to where the wildebeest are waiting.
Next, since we have two lions waiting, the only option is for two wildebeest to cross. There’s no point in sending two wildebeest back, as that would reverse the last step. If two lions go back, they would outnumber the wildebeest on the other side. So, one lion and one wildebeest take the raft back, leaving us with one of each animal on one side and two of each on the other.
Again, there’s no point in sending the lion-wildebeest pair back, so the next trip should be either a pair of lions or a pair of wildebeest. If the lions go, they would pose a threat to the wildebeest left behind, so they stay, and the two wildebeest cross instead.
Now, the wildebeest are all where they need to be with safety in numbers. All that’s left is for the remaining lion to return and bring the other lions over one by one. This makes a total of eleven trips, the smallest number needed to get everyone across safely.
The six animals escape the fire just in time and begin their new lives across the river. Now that the danger has passed, it remains to be seen how long their unlikely alliance will last.
Riddle – A question or statement that requires thought to answer or understand, often with a clever or surprising solution. – The teacher gave us a riddle about a mysterious creature that lives both in water and on land.
Animals – Living organisms that can move and respond to their environment, usually needing food to survive. – In biology class, we learned about different animals and how they adapt to their habitats.
River – A large, flowing body of water that usually empties into a sea or ocean. – The river was home to many fish and plants, providing a perfect example of an ecosystem.
Wildebeest – A large African antelope with a head like an ox and a long tufted tail. – During our lesson on migration, we watched a video of wildebeest crossing the plains in search of food.
Lions – Large, powerful carnivorous mammals known as the “king of the jungle,” living in groups called prides. – The lions worked together to hunt, demonstrating the importance of teamwork in the animal kingdom.
Raft – A flat structure used for floating or traveling on water, often made of logs or inflatable materials. – We built a small raft in science class to learn about buoyancy and how objects float.
Danger – The possibility of harm or injury. – The students discussed the danger animals face when their habitats are destroyed.
Crossing – The act of moving from one side to another, often over a barrier like a river or road. – The wildebeest faced many challenges while crossing the river during their migration.
Safely – In a way that avoids harm or risk. – The teacher explained how animals find ways to travel safely through dangerous areas.
Moves – Changes position or location, often in a deliberate or purposeful way. – The cheetah moves quickly to catch its prey, showing its incredible speed and agility.
