Annenberg Foundation
Annenberg Learner: Patterns in Mathematics: Mystery Operations
This interactive activity allows you to change an equation's numbers in an attempt to figure out what operations are being used to control the answers.
University of Cambridge
University of Cambridge: Nrich: 2, 4, 6, 8
On this one page website sharpen your logic, addition, and subtraction skills while working on this challenge. The solution is available to double check your solution.