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# Svetlana ran the first 5 kilometers of a 10-kilometer race a

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Retired Moderator
Joined: 07 Jun 2014
Posts: 4803
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
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Kudos [?]: 3029 [1] , given: 394

Svetlana ran the first 5 kilometers of a 10-kilometer race a [#permalink]  14 Jun 2018, 14:40
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Expert's post
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Question Stats:

83% (02:10) correct 16% (02:06) wrong based on 30 sessions
Svetlana ran the first 5 kilometers of a 10-kilometer race at a constant rate of 12 kilometers per hour. If she completed the entire 10-kilometer race in 55 minutes, at what constant rate did she run the last 5 kilometers of the race, in kilometers per hour?

(A) 15
(B) 12
(C) 11
(D) 10
(E) 8
[Reveal] Spoiler: OA

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Sandy
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Retired Moderator
Joined: 07 Jun 2014
Posts: 4803
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 175

Kudos [?]: 3029 [0], given: 394

Re: Svetlana ran the first 5 kilometers of a 10-kilometer race a [#permalink]  07 Jul 2018, 04:32
Expert's post
Explanation

To calculate Svetlana’s speed during the second half of the race, first calculate how long it took her to run the first half of the race. Svetlana ran the first 5 kilometers at a constant rate of 12 kilometers per hour.

These values can be used in the D = RT formula:

D(km)=R(km per hour) * T (hr)

Svetlana’s time for the first part of the race is $$\frac{5}{12}$$hours, or 25 minutes.

She completed the entire 10-kilometer race in 55 minutes, so she ran the last 5 kilometers in 55 – 25 = 30 minutes, or 0.5 hours. Now create another chart to find the rate at which she ran the last 5 kilometers:

5 = 0.5r
10 = r

Svetlana ran the second half of the race at a speed of 10 kilometers per hour.
_________________

Sandy
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Re: Svetlana ran the first 5 kilometers of a 10-kilometer race a   [#permalink] 07 Jul 2018, 04:32
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