To find out how many hours Mary rides her bike, we can use the formula:

$\text{Time} = \frac{\text{Distance}}{\text{Speed}}$

Given:

• Distance = 12.8 kilometers
• Speed = 8 kilometers per hour

Substituting the values:

$\text{Time} = \frac{12.8 \text{ km}}{8 \text{ km/h}} = 1.6 \text{ hours}$

So, Mary rides her bike for 1.6 hours.

Would you like more details or have any questions?

Here are some related questions:

1. How many minutes does Mary ride her bike?
2. If Mary increased her speed to 10 km/h, how long would it take her to ride 12.8 km?
3. What would be the time taken if Mary rode for 20 km at 8 km/h?
4. How far would Mary travel in 2 hours at a speed of 8 km/h?
5. If Mary maintained a speed of 8 km/h for 3 hours, how many kilometers would she cover?
6. How long would it take Mary to travel 25.6 kilometers at 8 km/h?
7. What is the average speed if Mary took 2 hours to cover 12.8 kilometers?
8. If Mary took 1 hour to cover half of the distance, what was her speed?

Tip: When dealing with distance, speed, and time problems, always remember the formula $\text{Time} = \frac{\text{Distance}}{\text{Speed}}$.