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# Cars J and K are making the trip from City A to City B. Car J departs

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Math Expert
Joined: 02 Sep 2009
Posts: 60627
Cars J and K are making the trip from City A to City B. Car J departs  [#permalink]

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13 Nov 2019, 06:05
00:00

Difficulty:

65% (hard)

Question Stats:

56% (02:04) correct 44% (02:57) wrong based on 70 sessions

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Cars J and K are making the trip from City A to City B. Car J departs from City A 15 minutes after Car K does, and both cars travel along the same route. If Car K travels at a constant speed that is 80% the constant speed of Car J, then how many minutes will elapse before Car J catches up to Car K?

A. 20
B. 45
C. 60
D. 75
E. 1230

Are You Up For the Challenge: 700 Level Questions

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Joined: 10 Dec 2017
Posts: 177
Location: India
Cars J and K are making the trip from City A to City B. Car J departs  [#permalink]

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13 Nov 2019, 06:21
Bunuel wrote:
Cars J and K are making the trip from City A to City B. Car J departs from City A 15 minutes after Car K does, and both cars travel along the same route. If Car K travels at a constant speed that is 80% the constant speed of Car J, then how many minutes will elapse before Car J catches up to Car K?

A. 20
B. 45
C. 60
D. 75
E. 1230

Are You Up For the Challenge: 700 Level Questions

Speed of Car J= X
Speed of Car K=0.8X
distance travelled by Car K in 15 minutes= 15*0.8X
=12X
So Car J will cover this 12X distance relative to Car K in time "t"
speed*time=distance
(X-0.8X)*t=12X
t=60 minutes
C:)
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Joined: 19 Oct 2018
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Re: Cars J and K are making the trip from City A to City B. Car J departs  [#permalink]

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13 Nov 2019, 14:19
$$V_J : V_K= 5:4$$

$$T_J : T_K= 4:5$$

$$T_K - T_J=5x - 4x=15$$

$$T_J= 4x= 4*15=60$$

Bunuel wrote:
Cars J and K are making the trip from City A to City B. Car J departs from City A 15 minutes after Car K does, and both cars travel along the same route. If Car K travels at a constant speed that is 80% the constant speed of Car J, then how many minutes will elapse before Car J catches up to Car K?

A. 20
B. 45
C. 60
D. 75
E. 1230

Are You Up For the Challenge: 700 Level Questions
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Joined: 21 Jun 2017
Posts: 396
Location: India
Concentration: Finance, Economics
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GMAT 1: 620 Q47 V30
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Cars J and K are making the trip from City A to City B. Car J departs  [#permalink]

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14 Nov 2019, 23:33
1
Then how many minutes will elapse before Car J catches up to Car K

(t+15)K = (t)J and K=(4/5)*J . Hence t is 60 . But we are asked of elapsed time so add 15 minutes to it. Answer = 60+15 = 75.
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Re: Cars J and K are making the trip from City A to City B. Car J departs  [#permalink]

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17 Nov 2019, 20:28
Bunuel wrote:
Cars J and K are making the trip from City A to City B. Car J departs from City A 15 minutes after Car K does, and both cars travel along the same route. If Car K travels at a constant speed that is 80% the constant speed of Car J, then how many minutes will elapse before Car J catches up to Car K?

A. 20
B. 45
C. 60
D. 75
E. 1230

Are You Up For the Challenge: 700 Level Questions

Let r = the speed of Car J, so 0.8r = the speed of Car K. Let’s also let t = Car J’s travel time, in hours; this means that (t + ¼) is Car K’s travel time (because 15 minutes = ¼ hour). We can create the equation:

Car K’s distance = Car J’s distance

(0.8r)(t + 1/4) = rt

0.8(t + 0.25) = t

0.8t + 0.2 = t

0.2 = 0.2t

1 = t

Since 1 hour = 60 minutes, choice C is the correct answer.

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Manager
Joined: 23 Jul 2015
Posts: 79
Re: Cars J and K are making the trip from City A to City B. Car J departs  [#permalink]

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17 Nov 2019, 22:15
1
Why isn't the answer 75? Don't have to count the 15 min delay as well?
Re: Cars J and K are making the trip from City A to City B. Car J departs   [#permalink] 17 Nov 2019, 22:15
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# Cars J and K are making the trip from City A to City B. Car J departs

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