Final answer:
To write an equation relating the time Juan spends riding at 12 mi/h and walking at 4 mi/h to travel 20 miles, we use the formula 'distance = speed × time' to set up the equation 12 * tr + 4 * tw = 20, where tr is the time spent riding and tw is the time spent walking.
Step-by-step explanation:
To relate the amount of time Juan spends riding or walking to travel 20 miles, let's introduce two variables: tr for the time spent riding his bike and tw for the time spent walking. We know that Juan's biking speed is 12 miles per hour (mi/h) and his walking speed is 4 mi/h.
Using the formula distance = speed × time, we can set up two equations representing the distance covered by each mode of transport:
- Biking distance: 12 * tr
- Walking distance: 4 * tw
Since the total distance is 20 miles, we can write:
12 * tr + 4 * tw = 20
This is Juan's equation in standard form relating the total time spent on riding and walking to cover 20 miles.