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Source: — Problem Solving |
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by parallel_chase » Sun Dec 28, 2008 6:51 am
Total distance = x

75%x/50 = T1

25%x/S = T2

T1+T2 = 75%x/50 + 25%x/S = (12Sx + 200x)/800S

X/(T1+T2) = 40

x / (12Sx + 200x)/800S = 40

800Sx = 480Sx + 8000x

320Sx = 8000x

cancel x from both sides

S = 8000/320 = 25

OA?
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by parallel_chase » Sun Dec 28, 2008 7:13 am
Here is another method: Pluggin In number

Let total distance = 100

75/50 = T1

25/S = T2

T1 + T2 = (75S + 1250)/50S

Avg. Speed = Total Distance/ Total time

40 = 100 /(75S + 1250)/50S


40 = 5000S / (75S +1250)

3000S + 50000 = 5000S

2000S = 50000

S = 25

Hope this helps.
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by vivek.kapoor83 » Sun Dec 28, 2008 8:58 am
25...solved by same method as above.
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by rajataga » Sun Dec 28, 2008 10:39 am
Yup, it is C....

I am surprised nobody made the mistake of taking average speed to be average speed over distance (it is actually over time)......I made that mistake when i first solved this sum :(
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