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Alex and Brenda both stand at point X. Alex begins to walk a

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Re: Alex and Brenda both stand at point X. Alex begins to walk a  [#permalink]

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New post 18 Jul 2017, 03:44
Marcab wrote:
Can you please let me know where am I committing mistake?
Alex already covered 4 miles. In the next t hours the total distance covered by Alex will be 4+4t.
Similarly Brenda covers Rt miles in the next t hours.
Therefore, Rt=2(4+4t)t
t=8/(R-8)


Even i committed the same mistake, you have considered the time, which Brenda has spent commuting, but the question asks the amount of time,Alex has spent walking, which is 1 hr more than what brenda has spent

so 8/r-8 +1 = r/r-8
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Re: Alex and Brenda both stand at point X. Alex begins to walk a  [#permalink]

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New post 11 Dec 2017, 09:54
enigma123 wrote:
Alex and Brenda both stand at point X. Alex begins to walk away from Brenda in a straight line at a rate of 4 miles per hour. One hour later, Brenda begins to ride a bicycle in a straight line in the opposite direction at a rate of R miles per hour. If R > 8, which of the following represents the amount of time, in terms of R, that Alex will have been walking when Brenda has covered twice as much distance as Alex?

A. R-4
B. R/(R+4)
C. R/(R-8)
D. 8/(R-8)
E. 2R - 4


We are given that Alex has a rate of 4 mph and Brenda has a rate of R mph. We are also given that Alex begins to walk away from Brenda in a straight line at a rate of 4 mph. One hour later, Brenda begins to ride a bicycle in a straight line in the opposite direction. Thus, we can let Alex’s time = T + 1 and Brenda’s time = T.

Finally, since distance = rate x time, Alex’s distance = 4(T + 1) = 4T + 4 and Brenda’s distance = RT. We need to determine the amount of time it takes Brenda to cover twice the distance Alex has gone. So, we can create the following equation and determine T:

2(4T + 4) = RT

8T + 8 = RT

8 = RT - 8T

8 = T(R - 8)

8/(R - 8) = T

Since we are asked for Alex’s time, T + 1 = 8/(R - 8) + (R - 8)/(R - 8) = R/(R - 8).

Answer: C
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Re: Alex and Brenda both stand at point X. Alex begins to walk a  [#permalink]

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New post 23 Jun 2018, 15:30
Let T be the time in which Brenda completed twice the distance as Alex.
D(A) = Distance Traveled by Alex in time T = 4*T = 4T
D(B) = Distance Traveled by Brenda in time T=> since Brenda started an hour later, it will be T-1. Distance Traveled = R*(T-1)

Now, per details in Question,
2* D(A) = D(B)
=> 2* 4T= R(T-1)
=> 8T = RT - R
=> T(R-8)=R
=> T= R/(R-8) {Option C}
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Re: Alex and Brenda both stand at point X. Alex begins to walk a  [#permalink]

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New post 07 Nov 2018, 14:47
Bunuel wrote:
enigma123 wrote:
Alex and Brenda both stand at point X. Alex begins to walk away from Brenda in a straight line at a rate of 4 miles per hour. One hour later, Brenda begins to ride a bicycle in a straight line in the opposite direction at a rate of R miles per hour. If R > 8, which of the following represents the amount of time, in terms of R, that Alex will have been walking when Brenda has covered twice as much distance as Alex?

A. R-4
B. R/R+4
C. R/R-8
D. 8/R-8
E. 2R - 4

Guys - I don't have an OA for this. Can you please help in terms of how this can be solved?


Let T be the time that Alex will have been walking when Brenda has covered twice as much distance as Alex.

In T hours Alex will cover 4T miles;
Since Brenda begins her journey 1 hour later than Alex then total time for her will be T-1 hours, and the distance covered in that time will be R(T-1);

We want the distance covered by Brenda to be twice as much as that of Alex: 2*4T=R(T-1) --> 8T=RT-R --> T=R/(R-8).

Answer: C.

Bunuel,
I found option D as anser. Let at T hrs, Brenda walked tice the distance.
RT= 2(4(t+1)
RT=8T + 8
RT-8T= 8
T= 8/(R-8)

Please help me on this.
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Re: Alex and Brenda both stand at point X. Alex begins to walk a &nbs [#permalink] 07 Nov 2018, 14:47

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