I am the tool, for inspiring many. Buy me in the store, for not much more than a penny. Don't overuse me, or my usefulness will go.
Answer: pen
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.