Difference between revisions of "2018 AMC 8 Problems/Problem 17"

Revision as of 01:18, 13 January 2023

Problem

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 $5$ times as fast as Bella walks. The distance between their houses is $2$ miles, which is $10,560$ feet, and Bella covers $2 \tfrac{1}{2}$ feet with each step. How many steps will Bella take by the time she meets Ella?

$\textbf{(A) }704\qquad\textbf{(B) }845\qquad\textbf{(C) }1056\qquad\textbf{(D) }1760\qquad \textbf{(E) }3520$

Solution 1

Since Ella rides 5 times faster than Bella, the ratio of their speeds is 5:1. For Bella, we have d/r = t and for Ella, we have d/5r = t; however, we know the times for both girls must be the same, and so that means in d/5r = t, the numerator becomes 5d (Ella travels 5 times the distance that Bella does). This means that Bella travels 1/6 of the way, and 1/6 of 10,560 feet is 1,760 feet. Bella also walks 2.5 feet each step, and 1,760 divided by 2.5 is $\boxed{\textbf{(A) }704}$ .

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 $10560\div60=176$ 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, $1760\div2.5=\boxed{\textbf{(A) }704}$

- 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 $\boxed{\textbf{(A) }704}$ .

Video Solution

https://youtu.be/ycZ381n_1bQ

~savannahsolver

https://www.youtube.com/watch?v=UczCIsRzAeo

@@ Line 10: / Line 10: @@
 ==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 <math>10560\div60=176</math> 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, <math>1760\div2.5=\boxed{\textbf{(A) }704}</math>
 - alexdapog A-A

2018 AMC 8 (Problems • Answer Key • Resources)
Preceded by Problem 16	Followed by Problem 18
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All AJHSME/AMC 8 Problems and Solutions

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