Complete Figure 3. You should:
• use a suitable scale for the y-axis
• plot the data from Table 2
• draw a line of best fit.
How to approach this question
1. **Choose a scale:** The y-axis needs to go up to at least 100. A simple scale would be to have every 2 large squares represent 20 units (so 0, 20, 40, 60, 80, 100). Label the axis.
2. **Plot points:** For each pair of values in Table 2, find the x-coordinate (blockage %) and the y-coordinate (blood flow) and mark a small, neat cross (x) or a point in a circle (⊙) at the correct position.
3. **Draw line of best fit:** The points form a curve. Draw a single, smooth curve that goes as close as possible to all the points. Do not join the dots with straight lines.
Full Answer
To complete the graph, you must first create a suitable scale for the y-axis. The maximum value for blood flow is 100, so a scale from 0 to 100 is appropriate. A linear scale (e.g., each major grid line represents 10 or 20 cm³/minute) must be used. The axis must be labelled "Blood flow in cm³/minute".
Next, plot the five data points from Table 2 accurately. For example, for the point (10, 64), find 10 on the x-axis and 64 on your new y-axis and mark the intersection.
Finally, draw a line of best fit. Since the points do not form a straight line, a smooth curve should be drawn that passes through or very close to all the plotted points, showing the overall trend.
Common mistakes
✗ Using a non-linear scale on the y-axis.
✗ Joining the points with straight, ruled lines (dot-to-dot).
✗ Drawing a straight line of best fit when the data clearly shows a curve.
✗ Not labelling the y-axis.
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