Logic Riddles

Question: Two brothers are twins. One twin says he is older than the other. The other twin is confused and says: in order for us to be twins we have to born on the same day. How is the one twin older than the other?

Question: there are 3 houses. a brown house a green house and white house. if the green house is in front of the brown house. and the brown house is in the back of the green house, Where is the white house?

Question: Like a middle pillar I stand among 6, all 9 of my characters make me the largest to exist.

Question: Keys! keys! So many keys, When F is involved The key note is _ ?

Question: You have 20 sick sheep, one dies. How many are left?