Staff chooses one file after feedback and a delay. Learners use the assigned source/task only. Capture this first response before its matching later page. All numbers and descriptions are original conceptual models, not actual investigation results.
F1 first
Source: Cube C has edge 4 mm; D has edge 8 mm. Area = 6a²; volume = a³; face-to-centre distance = a/2; SA/V = area/volume. Each has a supplied layer 1 mm deep at 5 min. Central edge = max(a − 2d, 0); fraction penetrated = 1 − (central edge/a)³; For this supplied interval, the layer starts at depth d_start = 0 mm when t_start = 0 min. Average front speed = Δdepth/Δtime = (d_end − d_start)/(t_end − t_start). This is the model's interval average, not a constant future speed, intrinsic diffusion coefficient or molecular flux. In a separate supplied endpoint file C has 70, 74, 78 s and D 130, 134, 138 s, with independent model samples. Material, solution and endpoint rule match; temperature and stirring are unknown. Imposed layers and endpoint times are separate model descriptions.
Task: Calculate both areas, volumes, ratios with units and centre distances, and distinguish total surface from surface per volume. Calculate both fractions and average front speed, explaining why fraction is not intrinsic speed. Calculate both endpoint means/ranges; give a bounded comparison, missing condition and concrete improvement. State whether an actual learner investigation occurred. Preserve first work before the later page.