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Speed Distance DS

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by ern5231 » Sat Aug 15, 2009 10:24 am
If a car travels a distance of 120 km then what is the average speed of the car?
(1) If the average speed of the car increases by 5 km/hr then the time is reduced by 0.5 hr.
(2) If the average speed is increased by 20%, time will be reduced by 25%.
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Source: — Data Sufficiency |
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by woo » Sat Aug 15, 2009 9:25 pm
IMO D.

average speed s = total distance travelled d / total time taken t

1) s+5=120/(t-0.5)

2) .2s=120/.85t

Since we also know that s=120/t

we can figure out what s is even with one of the conditions.
Last edited by woo on Mon Aug 17, 2009 6:55 am, edited 1 time in total.
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by imhimanshu » Sun Aug 16, 2009 3:59 am
IMO A..what is OA?
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by ern5231 » Sun Aug 16, 2009 8:05 pm
OA is A but i would ask for a lil more explanation.

A) Incase of A we get a quadratic equation(check attached pic)

B) My understanding for eliminating B :

120=1.2s*0.75*t
Now, we know s*t=120
120=1.2s*0.75*120/s
which results in cancellation of average speed s throughout so we cannot answer. Is it why we are eliminating this?
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by gauravgundal » Sun Aug 16, 2009 11:29 pm
I don't think that the equation would be a Quadratic one.
The distance traveled in both the case will be 120 k.m
For x=avg speed and t- time

120 =x.h
from A
we get,
120=(x+5)(1/2)h
so equating both we get value of x.
so A doesn't leads to a ny Quadratic equation.

Correct me if i am wrong
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