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Find the Bone
 
Q Ralph the dog can't remember where he buried his bone-under the rock, in the garden, under the porch, or under the tree. If only one of the following sentences is true, where is Ralph's bone?
  1. The bone is under the rock.
  2. The bone is in the garden or under the tree.
  3. The bone is under the rock or under the porch.
  4. The bone is not in the garden.


 
A The bone is in the garden.

If sentence #1 is true, then sentence #3 is also true, but only one sentence can be true, so both #1 and #3 are false-the bone is not under the rock or under the porch. That leaves the garden and the tree, so let's look at sentences #2 and #4. If sentence #2 is true, then sentence #4 is false. That would leave us with just 1 true sentence, but is the bone in the garden or under the tree? We know that sentence #4 is false, so the bone must be in the garden.

Source: Lowell House,Brain Games,p.60