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I am reposting the question below because none of the answers I received are...

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catd1115 | Middle School Teacher | (Level 3) Assistant Educator

Posted April 14, 2012 at 3:24 PM via web

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I am reposting the question below because none of the answers I received are correct/possible. The TOTAL has to be six miles in seven hours.

Juan jogs a certain distance and then walks a certain distance. When he jogs he averages seven miles per hour. When he walks, he averages 3.5 miles per hour. If he walks and jogs a total of six miles in a total of seven hours, how far does he jog and how far does he walk?

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justaguide | College Teacher | (Level 2) Distinguished Educator

Posted April 14, 2012 at 3:47 PM (Answer #1)

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Juan jogs at an average speed of 7 miles per hour, he walks at an average speed of 3.5 miles per hour. He walks and jogs for 7 hours in which duration he covers a total distance of 6 miles.

Let the time he jogs for be x hours; he walks for 7 - x hours. The distance traveled while he jogs is 7*x and the distance traveled while he walks is (7 - x)*3.5.

7x + (7 - x)*3.5 = 6

=> 7x + 24.5 - 3.5x = 6

This gives a negative value of x which is not possible.

Juan cannot cover a distance of 6 miles in 7 hours as his speed in this case would be 6/7 miles per hour. But he walks at a speed of 3.5 miles per hour. To travel 6 miles in 7 hours he would have to spend a part of the 6 hours at rest. In that case the time spent walking and the time spent jogging would not have a unique value.

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etotheeyepi | Student, Undergraduate | Valedictorian

Posted April 16, 2012 at 12:55 PM (Answer #2)

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We should say that the problem has a numerical answer that satisfies the given conditions, but it can only happen in the Twilight Zone.

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etotheeyepi | Student, Undergraduate | Valedictorian

Posted April 17, 2012 at 4:54 AM (Answer #3)

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Maybe this works.

let Juan walk for 5 hours or 17.5 miles.

Let Juan jog for 2 hours or 14 miles.

If the angle between walking and jogging is 0.312621419 radians, then the resulting displacement will be 6 miles by the law of cosines.

36 = 17.5^2 +14^2 - 2*17.5*14*cos(0.312621419 radians)

or the angle would be about 17.9 degrees.

 


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najm1947 | Elementary School Teacher | Valedictorian

Posted April 17, 2012 at 5:31 AM (Answer #4)

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The average speed during 6 hours Walk & Jog = 6/7 miles/hour

This speed is less than both the speeds i.e. Walk (7 miles/hour) and Jog (3.5 miles/hour). In this case the 7 hours target for 6 miles can be achieved only and only if:

1. One of the Walk/Jog average speed is less than 6/7 miles/hour and the other is more than 6/7 miles per hour

or

2. Both the average speeds for walk and jog are equal to 6/7 miles/hour

If both the average speeds are more than 6/7 miles per hour than there must be a rest period to make up the total time of 6 hours.

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