The answer is a play on words: Twice of ten is twenty. Twice of eleven is twenty too (two)!
Choose from a selection of wordplay puzzles to print and play offline on PuzzleChoice.com.
Of interest, Braingle, a brain teaser website, shared its most challenging riddles with BusinessInsider.com, as voted on by users.
Wake up your brain and give these a try. See how smart you are and solve these 15 impossible brain teasers.
Tip! Here are 8 ways to train your brain to learn faster and remember more shared by Lifehack.org.