Here are some resources based upon the Same Surface Different Deep problems, the theory of which is outlined in Craig Barton's book ''How I wish I' d taught maths''. There is already an excellent website where teachers from around the globe have contributed their versions of SSDD problems - I have merely made some of the ones I commonly use which regenerate with new numbers and mix up the position of the questions, so pupils are forced to carefully think about the question they are answering.