2018 AMC 8 Problems/Problem 17
Bella begins to walk from her house toward her friend Ella's house. At the same time, Ella begins to ride her bicycle toward Bella's house. They each maintain a constant speed, and Ella rides times as fast as Bella walks. The distance between their houses is miles, which is feet, and Bella covers feet with each step. How many steps will Bella take by the time she meets Ella?
Since Ella rides times faster than Bella, the ratio of their speeds is . For Bella, we have and for Ella, we have ; however, we know the times for both girls must be the same, and so that means in , the numerator becomes (Ella travels times the distance that Bella does). This means that Bella travels of the way, and of feet is feet. Bella also walks feet each step, and divided by is .
- by HunterHan
Solution 2 (Fast and Easy)
Every 10 feet Bella goes, Ella goes 50 feet, which means a total of 60 feet. They need to travel that 60 feet times to travel the entire 2 miles. SInce Bella goes 10 feet 176 times, this means that she travels a total of 1760 feet. And since she walks 2.5 feet each step,
~ alexdapog A-A
Solution 3 (Use Answer Choices to our advantage)
We know that Bella goes 2.5 feet per step and since Ella rides 5 times faster than Bella she must go 12.5 feet on her bike for every step of Bella's. For Bella, it takes 4,224 steps, and for Ella, it takes 1/5th those steps since Ella goes 5 times faster than Bella, taking her 844.8 steps. The number of steps where they meet therefore must be less than 844.8. The only answer choice less than it is .
We can turn into a mixed number. It will then become 5/2. Since Ella bikes 5 times faster, we multiply 5/2 by 5 to get 25/2. Then we add 5/2 to it in order to find the distance they walk and bike together in total. After adding, you should get 30/2 which is equal to 15. This means that after 15 times, they will meet. So you have to divide 10,560 by 15. The answer should be .
Video Solution (CREATIVE ANALYSIS!!!)
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