This task launches with a story retold by Ben Orlin about the famous detective Sherlock Holmes.

In Ben’s book, Change is the Only Constant (Orlin, 2019), he shares an extract from Sir Arthur Conan Doyle’s description of a calamity in a school. We took the Sherlock Holmes mystery and made it into a task, that we have found provokes students’ curiosity and creative thinking. In the beginning students are set a puzzle to solve – the delightful solution to which comes from the use of tangent lines. We recommend using the puzzle and time for students to explore as a reason to learn about tangent lines. Teachers often ask us: how do we present new content to students? We draw from research that has shown the best time to present content is after students have encountered a need for the content (Schwartz & Bransford, 1998). In this task students first explore the puzzle – which direction is the bike moving? – with different resources, and then pause to learn about tangent lines, or to revisit them if they have already met them. We have used this task both with students who have previously learned about tangent lines and appreciated a task that requires their use in a real situation, and with students who learned about tangent lines through this activity.