farooq wrote:A man walks by speed 2 KM/hr and cover 3/4 of total distance in 10 minutes and reaming distance in 30 minutes. What is the total distance ?
A. 400
B. 4.80
C. 360
D. 40
E. None
Ans - E.... but need explanation.....
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Two methods to calculate total average speed
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sankey014
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Ans - E.... but need explanation.....
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ilovemeforme123
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so I have this math homework im only in the 6th grade so here is the question I am having trouble about :::: the fastest running bird is the ostrich. An ostrich can run 240 miles in 6 hours. what is the average speed of an ostrich?????????
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Brent@GMATPrepNow
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Average speed = (total distance)/(total time)ilovemeforme123 wrote:so I have this math homework im only in the 6th grade so here is the question I am having trouble about :::: the fastest running bird is the ostrich. An ostrich can run 240 miles in 6 hours. what is the average speed of an ostrich?????????
= (240 miles)/(6 hours)
= 40 miles per hour
Alternatively we might apply some logic.
Traveling 240 miles in 6 hours is the same as traveling 120 miles in 3 hours, and traveling 120 miles in 3 hours is the same as traveling 40 miles in 1 hour (aka 40 miles per hour)
Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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praanavjayachandran
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I agree that the ratio logic was a bit confusing. I would like you to look at Mr Ashish's ratio approach in a different way.ajaygiri wrote:thank you ashish!
could not follow the ratio logic though, but the first one is crystal. thanks for the lucid explanation.
Suppose a and b be the two speeds (a>b). As mentioned, the average speed in this case is [2*(a*b)]/(a+b).
Just find the difference of the lower speed from this average speed.
[2*(a*b)/(a+b)]-a =a*[(b-a)/(a+b)]. This is exactly what Mr Ashish has added to the lower speed to get the final average speed, but explained in a different way.
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Matt@VeritasPrep
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That does seem a bit much, though: I wouldn't recommend memorizing formulas for unusual situations. It's better to get a sense of where averages come from, then (re)generate a useful approach like this when the situation demands it.
