Question

To find the unit rate of the train's speed, we need to determine how far the train travels in one hour. Based on the options given, let’s analyze each option to see which one represents a consistent unit rate.

1. **20 miles per 12 hours:**
To find the unit rate:
\( \frac{20 \text{ miles}}{12 \text{ hours}} = \frac{20}{12} = \frac{5}{3} \approx 1.67 \text{ miles per hour} \)

2. **20 miles per 1 half hour:**
This means the train travels 20 miles in half an hour. To find the rate for 1 hour, we double that:
\( 20 \text{ miles} \times 2 = 40 \text{ miles per hour} \)

3. **40 miles per hour:**
This is already provided as a unit rate.

4. **60 miles per hour:**
This is also provided as a unit rate.

5. **80 miles per 2 hours:**
To find the unit rate:
\( \frac{80 \text{ miles}}{2 \text{ hours}} = 40 \text{ miles per hour} \)

From the analysis, the consistent unit rate derived from the data is **40 miles per hour**, which appears in multiple instances.

The final answer is:
**40 miles per hour**