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# On a trip of 60 kilometres, Rita covered the first 15 kilometres

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Intern
Joined: 03 Mar 2018
Posts: 36
On a trip of 60 kilometres, Rita covered the first 15 kilometres [#permalink]

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05 Mar 2018, 07:58
00:00

Difficulty:

35% (medium)

Question Stats:

74% (03:02) correct 26% (01:50) wrong based on 19 sessions

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On a trip of 60 kilometres, Rita covered the first 15 kilometres at an average speed of 75 kilometres per hour and the following 35 kilometres at an average speed of 140 kilometres per hour. At what average speed did she cover the last part of her trip if her average speed for the whole trip was 80 kilometres per hour?

(A) 3 kilometres per hour

(B) 25 kilometres per hour

(C) 30 kilometres per hour

(D) $$\frac{100}{3}$$ kilometres per hour

(E) $$\frac{200}{3}$$ kilometres per hour
[Reveal] Spoiler: OA
Math Expert
Joined: 02 Aug 2009
Posts: 5713
Re: On a trip of 60 kilometres, Rita covered the first 15 kilometres [#permalink]

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05 Mar 2018, 09:10
1
KUDOS
Expert's post
itisSheldon wrote:
On a trip of 60 kilometres, Rita covered the first 15 kilometres at an average speed of 75 kilometres per hour and the following 35 kilometres at an average speed of 140 kilometres per hour. At what average speed did she cover the last part of her trip if her average speed for the whole trip was 80 kilometres per hour?

(A) 3 kilometres per hour

(B) 25 kilometres per hour

(C) 30 kilometres per hour

(D) $$\frac{100}{3}$$ kilometres per hour

(E) $$\frac{200}{3}$$ kilometres per hour

total time taken = $$\frac{60*60}{80}=45 min$$
time taken for first 15 km = $$\frac{15*60}{75} = 12 min$$
time taken for next 35 km = $$\frac{35*60}{140} = 15 min$$
so time taken for remaining 60-15-35 or 10 km is 45-12-15 or 18 min..
therefore speed in kmph = $$\frac{10*60}{18}=\frac{100}{3}$$

D
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Re: On a trip of 60 kilometres, Rita covered the first 15 kilometres   [#permalink] 05 Mar 2018, 09:10
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