It is a sound of empty, speak and it'll talk back plenty. But all the more you yack, you'll get the same words back.
Answer: echo
Select a pack of riddles and try to solve it in an interesting way.
This riddle appears in the following downloadable PDF files:
Einstein said that only 2% of the world could solve this problem. Can you do it?
Complete the grid by using logic and the given clues of each problem.
Use logic deductions to solve problems that are similar to the Einstein's Riddle.