Return to Current Week's Problems
Test your skills against the best!
The Challenge Mode provides you with a list of the most challenging problems for each contest. In the Challenge Mode, problems are ranked by the percentage of correct responses submitted for each problem. In other words, the smaller the percentage, the harder the problem is to participants. Only problems with 50% or less of correct responses are listed in the Challenge Mode. Test your knowledge by submitting answers to these past problems. Remember, you can still submit answers to any past problem. We will respond to your submission but your name will not be added to the list if your answer is correct.