Alex and Brenda both stand at point X. ALex begins to walk away from Branda in a straight line at a rate of 4 miles per hour. One hour later, Branda 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) R^2-4
While I understand the solution 2(4T) = R(T-1) leading to answer C, I do not understand why using T+1 for Alex's time (instead of T) and T for Brenda's time (instead of T-1) leads to a different response:
2[(4(T+1)]=RT
8T+8=RT
RT-8T=8
T= 8/(R-8)
Can someone please explain why is this (T for Alex and T-1 for Brenda) the right answer and what is the rationale for getting a different answer when I use T+1 and T for Alex and Brenda respectively?
Thanks.