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# A river boat leaves Silver Town and travels upstream to Gold Town at a

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Math Expert
Joined: 02 Sep 2009
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A river boat leaves Silver Town and travels upstream to Gold Town at a  [#permalink]

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14 Feb 2016, 04:44
1
6
00:00

Difficulty:

35% (medium)

Question Stats:

69% (01:35) correct 31% (01:38) wrong based on 251 sessions

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A river boat leaves Silver Town and travels upstream to Gold Town at an average speed of 6 kilometers per hour. It returns by the same route at an average speed of 9 kilometers per hour. What is the average speed for the round-trip in kilometers per hour?

A) 7.0
B) 7.1
C) 7.2
D) 7.5
E) 8.0

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Posts: 1
Re: A river boat leaves Silver Town and travels upstream to Gold Town at a  [#permalink]

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15 Feb 2016, 10:08
2
1
Pick a number which is LCM of 9 and 6 = 18.
Upstream time = 18/6 = 3 hrs
Downstream time = 18/9 = 2 hrs
Total time = 5 hrs
Total distance = 36
Average Speed = 36/5 = 7.2 km/hr
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Re: A river boat leaves Silver Town and travels upstream to Gold Town at a  [#permalink]

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15 Feb 2016, 15:22
2
1
let total distance=2d
total time=d/6+d/9=5d/18
2d/(5d/18)=36/5=7.2 km/hr
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Re: A river boat leaves Silver Town and travels upstream to Gold Town at a  [#permalink]

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04 Dec 2016, 20:29
Distances are going to be the same since it is a round-trip. Find an arbitrary value for the distance that can be used by both rates…aka find the multiple. 18 km works.

Then find the hours using D=RT.
18km = (9km/hr)(time) --> 2 hours
18km = (6km/hr)(time) --> 3 hours

Find the total distance and time to get the average speed.
(18km + 18km) / (2 hours + 3 hours) = 36/5 = 7.2 km/hrs

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Re: A river boat leaves Silver Town and travels upstream to Gold Town at a  [#permalink]

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26 Apr 2018, 15:20
Bunuel wrote:
A river boat leaves Silver Town and travels upstream to Gold Town at an average speed of 6 kilometers per hour. It returns by the same route at an average speed of 9 kilometers per hour. What is the average speed for the round-trip in kilometers per hour?

A) 7.0
B) 7.1
C) 7.2
D) 7.5
E) 8.0

We can let the distance = 18, so that the time upstream is 18/6 = 3 hours and the time downstream is 18/9 = 2 hours. Now we can determine average rate.

average rate = total distance/total time

average rate = 36/(3 + 2) = 36/5 = 7.2

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Re: A river boat leaves Silver Town and travels upstream to Gold Town at a  [#permalink]

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25 Jan 2019, 03:34
Bunuel wrote:
A river boat leaves Silver Town and travels upstream to Gold Town at an average speed of 6 kilometers per hour. It returns by the same route at an average speed of 9 kilometers per hour. What is the average speed for the round-trip in kilometers per hour?

A) 7.0
B) 7.1
C) 7.2
D) 7.5
E) 8.0

Average Speed = 2 a * b/ (a+b)

= 2 * 6 * 9 / 15
= 7.2

C
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A river boat leaves Silver Town and travels upstream to Gold Town at a  [#permalink]

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06 Mar 2019, 08:17
Bunuel wrote:
A river boat leaves Silver Town and travels upstream to Gold Town at an average speed of 6 kilometers per hour. It returns by the same route at an average speed of 9 kilometers per hour. What is the average speed for the round-trip in kilometers per hour?

A) 7.0
B) 7.1
C) 7.2
D) 7.5
E) 8.0

Note : When distances of both the legs are equal, the average speed equals

Avg. speed = $$\frac{2*a*b}{(a + b)}$$

Where "a" and "b" are individual speeds given.

Therefore, $$\frac{2*6*9}{6+9}$$

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A river boat leaves Silver Town and travels upstream to Gold Town at a   [#permalink] 06 Mar 2019, 08:17
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