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.

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