To determine the average gradient of the road descending the spur into Bobo town, we need to understand what gradient means and how to calculate it. The gradient is a measure of how steep a slope is, typically expressed as a ratio of vertical rise to horizontal run. Step-by-Step Explanation

1. Understanding Gradient:
2. The gradient is calculated using the formula: [ \text{Gradient} = \frac{\text{Vertical Rise}}{\text{Horizontal Run}} ]
3. This means for every unit of horizontal distance, how much vertical distance is gained or lost.
4. Interpreting the Options:
5. The options given (1:37, 1:42, 1:47, 1:52) represent the ratio of vertical rise to horizontal run. A gradient of 1:37 means that for every 37 units of horizontal distance, there is a 1 unit vertical change.
6. Calculating the Average Gradient:
7. To find the average gradient, we would typically need specific measurements of the vertical drop (rise) and the horizontal distance (run) of the road. However, since we are given options, we can infer the correct answer based on the context or typical values for such gradients.
8. A gradient of 1:52 indicates a relatively gentle slope, which is common for roads to ensure safety and comfort for vehicles.
9. Why Option D (1:52) is Correct:
10. A gradient of 1:52 suggests that for every 52 units of horizontal distance, there is a 1 unit vertical drop. This is a reasonable and safe gradient for a road, especially in a town setting where steep gradients can be hazardous.
11. Roads with steeper gradients (like 1:37 or 1:42) would be less common in urban areas due to safety concerns and the potential for vehicles to struggle with steep inclines.
12. Why Other Options are Incorrect:
13. Option A (1:37): This represents a steeper gradient, which may not be practical for a road leading into a town. Steeper gradients can lead to difficulties for vehicles, especially in adverse weather conditions.
14. Option B (1:42): Similar to option A, this is still a relatively steep gradient. While it is slightly less steep than 1:37, it is still not as gentle as 1:52, making it less likely to be the average gradient for a road.
15. Option C (1:47): This option is closer to the correct answer but still steeper than 1:52. It may be used in some contexts, but again, it is less common for roads in populated areas.

Common Pitfalls

• Misunderstanding Ratios: Students often confuse the meaning of the ratio. Remember, a lower second number (like in 1:37) indicates a steeper slope.
• Assuming All Roads Have the Same Gradient: Different types of roads (highways, local roads, etc.) have different average gradients based on their purpose and location.

Revision Summary

• The average gradient is calculated as the ratio of vertical rise to horizontal run.
• A gradient of 1:52 is gentle and practical for roads in urban areas.
• Steeper gradients (1:37, 1:42) are less common due to safety concerns.
• Always interpret ratios carefully to avoid confusion about steepness.

By understanding these concepts, you can better analyze and interpret gradients in geography, especially in the context of road design and safety.