Jack and Christina are standing 210 feet apart on a level surface. Their dog, Lindy, is standing next to Christina. At

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Jack and Christina are standing 210 feet apart on a level surface. Their dog, Lindy, is standing next to Christina. At the same time, they all begin moving toward each other. Jack walks in a straight line toward Christina at a constant speed of 3 feet per second and Christina walks in a straight line toward Jack at a constant speed of 4 feet per second. Lindy runs at a constant speed of 10 feet per second from Christina to Jack, back to Christina, back to Jack, and so forth. What is the total distance, in feet, that Lindy has traveled when the three meet at one place?

A. 105
B. 210
C. 280
D. 300
E. 420


OA D

Source: Princeton Review
Source: — Problem Solving |

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Let distance traveled by Jack = x
Let distance traveled by Christiana = y
Let the time taken for Jack and Christiana to meet in the middle = t


Jack walks at a constant speed of 3 feet per second, Christiana walks at a constant speed of 4 feet per second
Given that distance = speed * time for Jack and Christian to meet in the middle
x = 3t and y = 4t
since x + y is expected to be a total distance of 210 feet
3t + 4t = 210
7t/7 = 210/7
t = 30 seconds


The total distance traveled by Lindy for the 3 to meet at one place while Lindy is moving back and forth at a constant speed of 10 feet per second will be =>
Distance = speed * time
10 * 30
=300 feet


$$Answer\ =D$$