This puzzle, called Four Fours, was introduced in the British scientific journal Knowledge: An Illustrated Magazine of Science in 1881 and became widely known. Now it is available as an easy-to-play smartphone app.

This app is the perfect tool to stimulate your brain and test your logical thinking. Even those who are not good at math can enjoy it with total ease, while math lovers will appreciate the extra depth it offers.

Challenge yourself with puzzles anytime, anywhere on your smartphone and train your mathematical brain while having fun at the same time! It is completely free to play.

Can you solve the target number "73" hardest puzzles with no hints?