Two “Crack The Safe” activities on simultaneous equations: one on linear equations and one involving a quadratic or circle. These contain four questions but three possible answers for each question; this means that students can self-check their answers (are they in the list of possible answers?) whilst the teacher can help those who require it. I use these as starters and plenaries but that is obviously up to you with the wrong answers offering an opportunity for discussion about what I have done in order to get that solution. Typo corrected!