Marla starts running around a circular track at the same...

[swerve]

Marla starts running around a circular track at the same time Nicks start walking around the same circular track. Marla completes 32 laps around the track per hour and Nicks completes 12 laps around the track per hour. How many minutes after Marla and Nick begin moving will Marla have completed 4 more laps around the track than Nick?

A. 5
B. 8
C. 12
D. 15
E. 20

The OA is C.

Please, can any expert explain this PS question for me? I can't get the correct answer and I would like to know how to solve it in a quick way. I need your help. Thanks.

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Hi swerve,

We're told that Marla starts running around a circular track at the same time Nick start walking around the same circular track and that Marla completes 32 laps around the track per hour, while Nick completes 12 laps around the track per hour. We're asked for the number of MINUTES after Marla and Nick begin moving that Marla will have completed 4 more laps around the track than Nick. This question can approached in a number of different ways, depending on how you want to approach the math involved.

Since we know the number of laps that each person completes in 1 hour, we can think in those terms. Marla completes 32 laps and Nick completes 12 laps in 1 hour. Thus, Marla completes 32 - 12 = 20 laps more than Nick in 60 minutes. Both of their rates are constant, so the difference in each of their respective distances will increase at a constant rate - and we can use a ratio to answer the question:

20 laps/60 minutes = 4 laps/X minutes
20X = 240
X = 12

Final Answer: C

GMAT assassins aren't born, they're made,
Rich

[Scott@TargetTestPrep]

Marla starts running around a circular track at the same time Nicks start walking around the same circular track. Marla completes 32 laps around the track per hour and Nicks completes 12 laps around the track per hour. How many minutes after Marla and Nick begin moving will Marla have completed 4 more laps around the track than Nick?

A. 5
B. 8
C. 12
D. 15
E. 20

We can let b = number of boys and g = number of girls originally in the group. Thus, we have:

b/(g - 15) = 2/1

and

(b - 45)/(g - 15) = 1/5

Simplifying the first equation, we have:

b = 2(g - 15)

b = 2g - 30

Substituting this into the second equation, we have:

(2g - 30 - 45)/(g - 15) = 1/5

5(2g - 75) = g - 15

10g - 375 = g - 15

9g = 360

g = 40

Answer: B

[Brent@GMATPrepNow]

Marla starts running around a circular track at the same time Nicks start walking around the same circular track. Marla completes 32 laps around the track per hour and Nicks completes 12 laps around the track per hour. How many minutes after Marla and Nick begin moving will Marla have completed 4 more laps around the track than Nick?

A. 5
B. 8
C. 12
D. 15
E. 20

Let t = the time (in HOURS) that it takes Marla to complete 4 more laps than Nick.
So, after t hours, we can write: (Marla's lap count) = (Nick's lap count) + 4

Now that we have a "word equation" we need only fill in the missing information

Marla completes 32 laps per hour
We can think of 1 lap as being a unit of distance.
So, 32 laps per hour is Marla's speed.

Distance = (speed)(time)
So, after t hours, Marla's lap count = 32t


Nick completes 12 laps around the track per hour
So, after t hours, Nick's lap count = 12t

We can now plug the above values into the word equation.
We get: 32t = 12t + 4
Subtract 12t from both sides to get: 20t = 4
Solve: t = 4/20 = 1/5 HOURS

1/5 hours = 12 minutes.

Answer: C

Cheers,
Brent