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This is how I solved this..

10s/2h, 72/2 -> 36 (and then the /h value x10) -> 36x10 = 360. Go on with /6 -> 6min
5s/3h, 72/3 -> 24 (and then the /h value x5) -> 36x5 = 120. Go on with /6 -> 2 (sine it's a loss it's -2)

-2 to 6 = 8, hence E (I did not get it right first since I personally missed the "loss")
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Bunuel,

This question is using a kind of Relative velocity fundamental, but is put forward in a different manner. Opposite speeds do add up in relative calculations.
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Bunuel,

Can you Please solve this question.

Pat's watch gains an extra 10 seconds every 2 hours. Kim's watch loses 5 seconds every 3 hours. If both watches are set to correct time at 8 o'clock in the morning and run without interruption, after 72 hours, what will be the difference in time between Pat's watch and Kim's watch?

(A) 4 min

(B) 6 min

(C) 6 min 40 sec

(D) 7 min 30 sec

(E) 8 min

In 72 hours Pat's watch will gain an extra 72/2*10 = 360 seconds.

In 72 hours Kim's watch will lose 72/3*5 = 120 seconds.

Hence the difference will be 360 + 120 = 480 seconds or 8 minutes.

Answer: E.

Hope it helps.
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megafan
Pat's watch gains an extra 10 seconds every 2 hours. Kim's watch loses 5 seconds every 3 hours. If both watches are set to correct time at 8 o'clock in the morning and run without interruption, after 72 hours, what will be the difference in time between Pat's watch and Kim's watch?

(A) 4 min

(B) 6 min

(C) 6 min 40 sec

(D) 7 min 30 sec

(E) 8 min

watch P gains 5 sph
watch K loses 5/3 sph
5+5/3=20/3 sph
72 h*20/3 sph=480 s
480 s/60 spm=8 min
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megafan
Pat's watch gains an extra 10 seconds every 2 hours. Kim's watch loses 5 seconds every 3 hours. If both watches are set to correct time at 8 o'clock in the morning and run without interruption, after 72 hours, what will be the difference in time between Pat's watch and Kim's watch?

(A) 4 min

(B) 6 min

(C) 6 min 40 sec

(D) 7 min 30 sec

(E) 8 min

In every 6 hours, Pat GAINS (10 + 10 +10) = 30 seconds

In every 6 hours, Kim LOSES (5 + 5) = 10 seconds or "GAINS" (-10) seconds

In every 6 hours, the time difference ==> 30 - (-10) = 40 seconds

In 72 hours, time difference ==> 72hrs/6hrs * 40 seconds = 480 seconds or 8 minutes

(E)
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megafan
Pat's watch gains an extra 10 seconds every 2 hours. Kim's watch loses 5 seconds every 3 hours. If both watches are set to correct time at 8 o'clock in the morning and run without interruption, after 72 hours, what will be the difference in time between Pat's watch and Kim's watch?

(A) 4 min

(B) 6 min

(C) 6 min 40 sec

(D) 7 min 30 sec

(E) 8 min


Pat's watch = 2 hrs ---- 10 seconds addition

72 hours ---- 360 seconds gain

Kim's watch ---- 3 hrs --- 5 seconds loss

72 hours ---- 120 seconds loss

Difference = 360 - ( - 120)

= 480/60

8 minutes
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Pat's watch gains an extra 10 seconds every 2 hours. Kim's watch loses 5 seconds every 3 hours. If both watches are set to correct time at 8 o'clock in the morning and run without interruption, after 72 hours, what will be the difference in time between Pat's watch and Kim's watch?

Pat:
After 72 hours i.e after 36 intervals, PAT's watch would have gained 6 minutes [ 10 seconds every 2 hours , so in 36 intervals , 360 seconds]

Kim:
Loses 5 seconds every 3 hours. In 72 hours i.e loses 5 seconds 24 times , that is equal to 2 minutes.

Pat's clock gains 6 minutes and kim's watch loses 2 minutes.

So time difference between watches is 8 Minutes

Ans: E
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megafan
Pat's watch gains an extra 10 seconds every 2 hours. Kim's watch loses 5 seconds every 3 hours. If both watches are set to correct time at 8 o'clock in the morning and run without interruption, after 72 hours, what will be the difference in time between Pat's watch and Kim's watch?

(A) 4 min

(B) 6 min

(C) 6 min 40 sec

(D) 7 min 30 sec

(E) 8 min

Pat’s watch gains 10 x 72/2 = 10 x 36 = 360 seconds in 72 hours.

Kim’s watch loses 5 x 72/3 = 5 x 24 = 120 seconds in 72 hours. We have to consider this as -120 since it’s the number of seconds lost.

Thus, the difference is 360 - (-120) = 480 seconds = 8 minutes.

Answer: E
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­Lovely little net rate problem:

­
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