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Marla starts running around a circular track at the same [#permalink]
 16 Mar 2012, 07:55
Question Stats:
74% (02:02) correct
26% (01:25) wrong based on 5 sessions
Marla starts running around a circular track at the same time Nick starts walking around the same circular track. Marla completes 32 laps around the track per hour and Nick 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 How to do this guys?
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Re: Marla starts running around a circular track at the same [#permalink]
16 Mar 2012, 09:26
1
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Re: Marla starts running around a circular track at the same [#permalink]
16 Mar 2012, 11:00
Marla completes 32laps/60min, Nick completes 12laps/60mins.
After x mins Marla would have completed 4 laps more than Nick had completed.
x((32-12)/60) = 4,
x*20/60 = 4,
x = 12 mins.
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Director
Status: Preparing for the 4th time -:(
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Re: Marla starts running around a circular track at the same [#permalink]
16 Mar 2012, 16:46
Bunuel - how did you get this? Marla to complete 4 (20/5=4) more laps will need 1/5 hours, which is 12 minutes.
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Re: Marla starts running around a circular track at the same [#permalink]
16 Mar 2012, 16:53
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Re: Marla starts running around a circular track at the same [#permalink]
17 Mar 2012, 07:06
Best way is to use plug in!
Always plug in C first, since this is the median value!
In 12 minutes she will have completed 32/5 rounds ( /5 because 12min is 1/5 hours) and he will have completed 12/5 rounds.
32/5 = 6 2/5
12/5 = 2 2/5
4 is the difference and hence C is th answer.
Sometimes you get lucky and plug in the right answer first! Will help you save heaps of time!
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Re: Marla starts running around a circular track at the same [#permalink]
12 Apr 2012, 04:35
Maria's rate - 32 laps per hour --> 32/60 laps/min
Nick's rate - 12 laps per hour --> 12/60 laps/min
lets set equations:
32/60*t=4 (since Maria had to run 4 laps before Nick would start)
12/60*t=0 (Hick has just started and hasn't run any lap yet)
-----------------------------------
(32/60-12/60)*t=4-0 (since Nick was chasing Maria)
t=12 min needed Maria to run 4 laps
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Marla starts running around a circular track at the same [#permalink]
23 Apr 2012, 15:00
Marla starts running around a circular track at the same time Nick starts walking around the same circular track. Marla completes 32 laps around the track per hour and Nick 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 Source: http://www.gmathacks.com
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Re: Marla starts running around a circular track at the same [#permalink]
23 Apr 2012, 15:27
I say C. 12 mins.
Marla's speed : 32/60 laps per min
Nick's speed : 12/60 laps per min
So by plugging in ans choices,
at 12 mins, Marla : 6.4 laps, Nick 2.4 laps.
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Re: Marla starts running around a circular track at the same [#permalink]
23 Apr 2012, 21:50
I also got C (12). t= time 32 laps per hour * t = 12 laps per hour * t + 4 laps 32t = 12t + 4 20t = 4 t= 1/5 hr 1/5(60min)= 12 mins I believe the recommended strategy is to change to minutes right away but in this situation I found it easier to do it at the end because of how the rates simplified per minute.
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Re: Marla starts running around a circular track at the same [#permalink]
23 Apr 2012, 22:28
In 15 min - Marla has completed 32/4 = 8 laps and Nick -> 12/4 = 3
the difference at 15 mins is 5 laps. So plugging in C.
In 12 mins - Marla has completed 32/5 = 6.4laps while Nick has completed 12/5 = 2.4 laps , a difference of 4 laps.
So ans - C
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Re: Marla starts running around a circular track at the same [#permalink]
23 Apr 2012, 23:32
In 1 min:
Marla runs: 32/60 = 8/15 laps
Nick walks: 12/60 = 1/5 laps
Let x be the number of minutes required for Marla to be 4 laps ahead of Nick.
x * 1/5 + 4 = x * 8/15
x =12 mins
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Re: Marla starts running around a circular track at the same [#permalink]
24 Apr 2012, 12:59
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Re: Marla starts running around a circular track at the same [#permalink]
25 Apr 2012, 02:21
The answer is C
use relative velocity to solve it
the relative velocity would be (32-12) in 1 hour.
hence, 20 laps in 1 hour
therefore time to complete four laps is 1/5hr
12 mins
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During a 40-mile trip, Maria traveled at an average speed of [#permalink]
19 Mar 2013, 19:04
During a 40-mile trip, Maria traveled at an average speed of x miles per hour for the first y miles of the trip and at an average speed of 1.25x miles per hour for the last 40-y miles of the trip. The time that Maria took to travel the 40 miles was what percent of the time it would have taken her if she had traveled at an average speed of x miles per hour for the entire trip?
1) x=48
2) y=20
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Re: During a 40-mile trip, Maria traveled at an average speed of [#permalink]
19 Mar 2013, 19:09
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Re: During a 40-mile trip, Maria traveled at an average speed of
[#permalink]
19 Mar 2013, 19:09
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