Jane drove at a constant speed from point A to point B and back to

Question

Jane drove at a constant speed from point A to point B and back to point A in 20 minutes. In how much time did Jacob drive from point B to point A?

(1) Jacob drove at a constant speed of 80 Km/h 
 (2) Jacob took 15 seconds less than Jane to drive through 1 km.

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prantorboni · Answer

Jane drove at a constant speed from point A to point B and back to point A in 20 minutes. In how much time did Jacob drive from point B to point A?

(1) Jacob drove at a constant speed of 80 Km/h. 
 Since the distance between A to B is unknown, we are unable to determine how much time Jacob takes to drive from point B to A using this information. So, Insufficient.

(2) Jacob took 15 seconds less than Jane to drive through 1 km. 
 How much time Jane takes to drive through 1 Km is unknown. So, this information is also Insufficient.

Now, consider both the information together,  
 Jacob drove at a constant speed of 80 Km/h. So, 80 Km in 3600 seconds and 1 Km in 3600/80=45 seconds. 
 Now, Jacob took 15 seconds less than Jane to drive through 1 km. So, Jane drive through 1 Km in 60 seconds or in 1 minute.

We are also aware that Jane drove at a constant speed from point A to point B and back to point A in 20 minutes. So, Jane drove 20x1=20 Km in 20 minute. So, the distance between A to B or B to A is 20/2= 10 Km.

Certainly, time taken by Jacob to drive from point B to A is= 10 x 45/60 minute= 10x3/4=7.5 minute. Sufficient.

Answer : C.

pierjoejoe · Answer

d 
 s 
 t 
 
  Jane 
 2x 
 d/t = 3x 
 2/3 hours 
 
  Jacob 
 x 
 y 
 z

we want z = x/y --> thus we want both x and y

(1) y = 80 NS

(2) Jacob takes 15 seconds longer than Jane to travel a distance of 1

Jacob's time - Jane's time = 15/3600
Jacob's time = 1/y --> time to travel 1 kilometer for Jacob
 Jane's time = 1/3x --> time to travel 1 kilometer for Jane

1/3x - 1/y = 15/3600 NS

(1)(2) 
we know both

1/3x - 1/y = 15/3600 
 y = 80

thus we have y and can find x from the first of the two equations. SUFFICIENT

pappal · Answer

the question stem just tells that Jake travelled 2*d distance (where d=distance from A to B) at constant speed in 1/3 hr. 
need to find time taken by Jacob to travel d distance (from B to A)=?
1. given Jacob's speed=80kmph  not sufficient  as d not known.
2. just gives the algebraic relation between the times taken by Jake and Jacob to travel the 1km.
this suggests its sufficient to relate their speeds algebraically, not their ratio. hence  insufficient  
however together,
we can find the speed of Jake which together with question stem is  sufficient  to find d and in turn time for Jacob to travel d.
C

Jane drove at a constant speed from point A to point B and back to

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GMAT Data Sufficiency (DS) Questions

Jane drove at a constant speed from point A to point B and back to

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