Question 21 of 37advanced🔍 AnalyzeLong Answer3 marks

A boatman wants to cross a river in a boat. He has to take a lion, a sheep, and a bundle of grass with him. He can take one of them at a time. If the sheep and grass are left on the shore, the sheep will eat the grass. And, if the sheep and lion are left on the shore, the lion will eat the sheep. How can the boatman take the lion, sheep, and grass across the river?

Correct Answer

Step 1: Take the sheep across first (lion and grass remain on starting shore - safe).

Step 2: Return alone to the starting shore.

Step 3: Take the lion across.

Step 4: Bring the sheep back to the starting shore (so lion doesn't eat sheep).

Step 5: Take the grass across.

Step 6: Return alone to the starting shore.

Step 7: Take the sheep across.

Now all three (lion, sheep, grass) are safely on the other shore.

Why it works: This is a classic river crossing puzzle. The key insight is that the sheep cannot be left alone with either the lion or the grass. The solution requires 7 trips total: the sheep must be transported first, then when the lion is taken, the sheep must be brought back to prevent it from being eaten, then the grass is taken, and finally the sheep is taken again.

Exercise: Pastime Mathematics | Q: 1 | (Page Page 11)
For More Understanding

Explanation

This is a classic river crossing puzzle. The key insight is that the sheep cannot be left alone with either the lion or the grass. The solution requires 7 trips total: the sheep must be transported first, then when the lion is taken, the sheep must be brought back to prevent it from being eaten, then the grass is taken, and finally the sheep is taken again.

Solution Steps

  1. Step 1: Take sheep across (lion + grass safe on shore 1)

  2. Step 2: Return alone

  3. Step 3: Take lion across

  4. Step 4: Bring sheep back (lion alone on shore 2)

  5. Step 5: Take grass across

  6. Step 6: Return alone

  7. Step 7: Take sheep across - all safe on shore 2

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