This is MGMAT's challenge problem of the week. Have fun !

Question

This is MGMAT's challenge problem of the week. Have fun ! :wink: 

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?

ps_dahiya · Answer

Let time "Alex will have been walking" = t

Distance covered by Alex = 4t
Distance covered by Brenda = R (t-1)

4t * 2 = R(t-1)
 t = R/(R-8)

giddi77 · Answer

too fast dahiya!

same answer. 

x = 4t
2x = R(t-1) solving for t we get

 t = R/(R-8)

allabout · Answer

Can someone please solve the following explicitly? 

4t * 2 = R(t-1)

giddi77 · Answer

Isn't it:

8*t = R*t - R
Since R>8,

R*t-8*t = R
t (R-8) = R
ot t = R/(R-8)

hkm_gmat · Answer

Let the time reqd be t ,

2(4+ 4t) = Rt
t = 8/(R-8)

allabout · Answer

Thanks giddi

Don't know why I couldn't make it too.

giddi77 · Answer

hkm_gmat, didn't you calculate the time that Brenda took. They have asked for time that Alex took. So 1 needs to be added to your answer.

T(Alex) = 8/(R-8) + 1
 = R/(R-8) 

Is my reasoning OK?

ywilfred · Answer

I've got the same :-D

. The OE for this question is not out yet, but I'm pretty sure all of us breezed through this one.

andy_gr8 · Answer

I too got R/ R-8 but took almost 4 min

This is MGMAT's challenge problem of the week. Have fun !

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