Dina and Masha started out on a 20-mile bike path at the same time. When Dina reached the end of the 20 miles, Masha still had 4 miles left to bike. If Dina’s biking speed was 10 mph, find Masha’s biking speed.
The correct answer and explanation is:
Correct Answer: Masha’s biking speed is 8 mph.
Step-by-Step Solution:
Let’s define what we know from the problem:
- Dina travels 20 miles at a speed of 10 mph.
- Time Dina takes to complete the path = Time=DistanceSpeed=2010=2 hours\text{Time} = \frac{\text{Distance}}{\text{Speed}} = \frac{20}{10} = 2 \text{ hours}
So, Dina bikes for 2 hours.
During the same 2 hours, Masha still has 4 miles left of the 20-mile path. That means she only covered: 20−4=16 miles20 – 4 = 16 \text{ miles}
in 2 hours.
Let’s use the formula for speed: Speed=DistanceTime=162=8 mph\text{Speed} = \frac{\text{Distance}}{\text{Time}} = \frac{16}{2} = 8 \text{ mph}
Final Answer:
8 mph\boxed{8 \text{ mph}}
300-Word Explanation:
To find Masha’s speed, we use the fundamental relationship between distance, speed, and time, which is: Speed=DistanceTime\text{Speed} = \frac{\text{Distance}}{\text{Time}}
In this scenario, both Dina and Masha started biking at the same time on the same 20-mile path. However, when Dina completed the 20 miles, Masha still had 4 miles left. This means that Masha had completed only 16 miles during the time it took Dina to bike 20 miles.
Dina’s speed is given as 10 miles per hour (mph), so the time it took her to complete 20 miles is: 20 miles10 mph=2 hours\frac{20 \text{ miles}}{10 \text{ mph}} = 2 \text{ hours}
Since both riders started at the same time and Dina took 2 hours to finish, Masha also had biked for 2 hours by that point.
Now, Masha covered 16 miles in those same 2 hours. Using the formula for speed: Masha’s Speed=16 miles2 hours=8 mph\text{Masha’s Speed} = \frac{16 \text{ miles}}{2 \text{ hours}} = 8 \text{ mph}
This method shows how comparison and logical reasoning can help solve problems involving motion. It’s crucial to align the time for both individuals to make the comparison fair. Hence, Masha’s biking speed is 8 mph.