RI Promos Solns 2025

RAFFLES INSTITUTION 2025 Year 5 H2 Mathematics Promotion Examination Questions and Solutions with comments ______________________ 2025 Yr 5 H2 Math Promotion Examination Solution with Comments General Comments • Wrong Exam Index Numbers A small number of students wrote the wrong Exam Index Number on their scripts, though fewer than during the Timed Practice. For example, 260227 was mistakenly written as 262027, which belongs to another student. 跚跛跜距 Please double-check your Index Number before writing it down in future assessments. • Writing Outside the Designated Boxes Quite a significant number of scripts had solutions written outside the boxes provided for each part of the question. 굓굔굕굖 For the actual A-Level exams, your scripts will be digitally scanned, and any writing outside the boxes may not be captured. 跚跛跜距 Always keep your work within the provided boundaries. • Writing Solutions in the Wrong Question Space More students than in the Timed Practice wrote solutions for one question in the space meant for another question. 跚跛跜距 Do not do this — different markers may be assigned to different questions, and your answer may be missed if it is in the wrong section. • Using Additional Pages and not using the correct Additional Page. A significant number of students who used Additional Pages did not indicate this on the original allocated space. There are also a few students wrote solutions on the provided school foolscap paper and submitted together with the answer booklet 跚跛跜距 When you use an Additional Page, always write “See Additional Page” clearly in the allocated space, or the marker may miss your continued work. 跚跛跜距 The provided school foolscap paper is meant for rough work. Any work that needs to be submitted for marking should be inside the Answer Booklet or the Additional Page. • Multiple Solutions for the Same Question Some students wrote two or three different solutions for the same question without cancelling the undesired ones. 跚跛跜距 You must cancel any solution that you do not want to be marked. The marker will only mark 1 solution. • Presentation and Legibility Most scripts were well presented, with clear and logical mathematical arguments. 踀踁 However, some scripts were difficult to mark because:  handwriting was hard to read  writing was too small  ink was too light  Reminder: Markers can only award marks for work that is legible. Please ensure your handwriting is neat, written at a reasonable size, and clearly visible.

2 ______________________ 2025 Yr 5 H2 Math Promotion Examination Solution with Comments 1 Fig. 1 A tablet is dissolving in water and is modelled as a cylinder, as shown in Fig. 1. At t seconds after being dropped into the water, the radius of the tablet is x mm, and its thickness is 1 3xmm. The circular cross-sectional area of the tablet is decreasing at a constant rate of 0.5 mm² per second. When x = 5, find the exa