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# Jack and Jill are marathon runners. Jack can finish a marathon (42 km)

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Math Expert
Joined: 02 Sep 2009
Posts: 52122
Jack and Jill are marathon runners. Jack can finish a marathon (42 km)  [#permalink]

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08 Dec 2015, 02:12
2
4
00:00

Difficulty:

25% (medium)

Question Stats:

78% (01:15) correct 22% (01:54) wrong based on 283 sessions

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Jack and Jill are marathon runners. Jack can finish a marathon (42 km) in 4.5 hours and Jill can run a marathon in 4.2 hours.What is the ratio of their average running speed? (Jack: Jill)

A. 14/15
B. 15/14
C. 4/5
D. 5/4
E. Cannot be determined

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Jack and Jill are marathon runners. Jack can finish a marathon (42 km)  [#permalink]

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Updated on: 08 Dec 2015, 04:07
1
speed is inversely proportional to time
or
s1/s2=t2/t1
t1/t2=4.5/4.2=s2/s1
therefore.
Jack/jill=14/15

Originally posted by CounterSniper on 08 Dec 2015, 02:28.
Last edited by CounterSniper on 08 Dec 2015, 04:07, edited 2 times in total.
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Re: Jack and Jill are marathon runners. Jack can finish a marathon (42 km)  [#permalink]

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08 Dec 2015, 03:24
Average Speed of Jack =Distance/ Time
= 42 /(9/2) = 84/9

Average Speed of Jill = 42/(4.2) = 10

Ratio of Average speed of Jack to Jill = (84/9)/10 = 84/90 = 14/15

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Re: Jack and Jill are marathon runners. Jack can finish a marathon (42 km)  [#permalink]

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08 Dec 2015, 03:48
jack speed =42/4.5

jill speed = 42/4.2

jack speed : jill speed 4.2 :4.5 =14/15
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Re: Jack and Jill are marathon runners. Jack can finish a marathon (42 km)  [#permalink]

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08 Dec 2015, 03:48
jack speed =42/4.5

jill speed = 42/4.2

jack speed : jill speed 4.2 :4.5 =14/15
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Re: Jack and Jill are marathon runners. Jack can finish a marathon (42 km)  [#permalink]

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09 Apr 2016, 13:26
distance being the same for both the runners jack and jill. Ratio of speeds of jack to jill's speed will be inverse of ratio of time required by them to complete the marathon
(Jill's Time/Jack's Time) - 4.2/4.5 = 14/15
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Re: Jack and Jill are marathon runners. Jack can finish a marathon (42 km)  [#permalink]

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24 Jun 2017, 07:14
1
$$R= \frac{D}{T}$$
Rate of Jack = $$\frac{42}{4.5}$$ and Rate of Jill = $$\frac{42}{4.2}$$

$$\frac{Jack}{Jill}=\frac{420}{45} * \frac{42}{420}$$ = $$\frac{42}{45} = \frac{14}{15}$$

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Re: Jack and Jill are marathon runners. Jack can finish a marathon (42 km)  [#permalink]

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22 Dec 2018, 19:01
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: Jack and Jill are marathon runners. Jack can finish a marathon (42 km) &nbs [#permalink] 22 Dec 2018, 19:01
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