Crack The Safe - Standard Form and Surds

Three “Crack The Safe” activities on standard form and surds (one on simplifying and one on expanding brackets and rationalising the denominator). These contain six questions but six possible answers for each question meaning 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.