Two trains are headed along parallel tracks in the same direction at

Question

Two trains are headed along parallel tracks in the same direction at varying rates of 72 mph and 47 mph. In how many hours will the faster train be 100 miles in front of the slower train?

(A) 2

(B) 2.5

(C) 3.5

(D) 4

(E) Cannot be determined by information provided.

pushpitkc · Answer

Since the trains are travelling in the same direction, the relative speed is x1 - x2 
if x1 and x2 are the speeds of both the trains.

Given data : x1 = 72mph, x2 = 47 mph
Relative speed = 72-47 = 25mph

To get 100 miles ahead, both the trains would have to travel 4 hours.(Option D)

K_Leon · Answer

D=R*T

Distance traveled of Train 1 after T hours is 72*T
Distance traveled of Train 2 after T hours is 27*T
After T hours, Train 1 has gained 100 miles more: 72T-27T = 100 --> T=4

rhtmhjn · Answer

Answer cannot be determined as we don't know initial positions of trains relative to each other. Answers posted would work if both the trains started from the same point and at the same time. Hence E

cbh · Answer

Thought the same, however answered D..will wait for the formal response.

Arsh4MBA · Answer

As the realtive speed is 25mph. In an hr the fast train will be 25 miles ahead. So to cover 100 miles the fast train needs 4 hrs.

Ans:D

ScottTargetTestPrep · Answer

Let t = the time in hours the two trains have traveled when the faster train is 100 miles ahead of the slower train. So, the distances traveled by the faster train and slower train are 72t and 47t, respectively, and we can create the following equation:

72t = 47t + 100

25t = 100

t = 4

Answer: D

elenysuk1 · Answer

t=time, r=rate
when the difference between the distances will be 100:
d=tr, we are looking for d1-d2=100 => t*r1-t*r2=100, 72t-47t=100, t=4 => D

dvishal387 · Answer

Since the trains are headed in same direction we can simply subtract the speeds and divide the distance by that
i.e 100/(72-47)=4 hours
D should be the correct choice.

Sent from my Redmi Note 3 using  GMAT Club Forum mobile app

hasnain3047 · Answer

speed of train 1=72 miles/hour
speed of train 2=47 miles/hour
relative speed =72-47 = 25
so time when faster train is ahead by 100 miles = 100/25 = 4hours

sumit411 · Answer

Initial separation=100 miles
Since the are traveling in the same direction, we have to subtract the relative speed

Time = initial separation/ relative speed
 = 100/25
 = 4 hours

Sent from my ONEPLUS A3003 using  GMAT Club Forum mobile app

Archit3110 · Answer

let time = t
72*t=47*t+100
t= 100/25 ; 4 hrs
IMO D

sony1000 · Answer

VERY GOOD POINT!!
VERY GOOD POINT!!
VERY GOOD POINT!!

Two trains are headed along parallel tracks in the same direction at

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Problem Solving (PS) Questions

Two trains are headed along parallel tracks in the same direction at

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards