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28 Jan 2009, 10:56
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Question: How much time did it take a certain car to travel 400km?
If the car's avg speed had been 20km/hr greater than it was, it would have traveled the 400km in 1hr less time than it did. How is this sentence sufficient?
Answer: let v be the original speed and t be the original time.
(v+20)*(t-1) = 400
vt=400 =>v=400/t
Thus, you can solve for t.
Followup: But the solution t still includes another variable v? So you can not find a finite answer for t, the answer for t will always include the unknow variable v, wont it?
If the car's avg speed had been 20km/hr greater than it was, it would have traveled the 400km in 1hr less time than it did. How is this sentence sufficient?
Answer: let v be the original speed and t be the original time.
(v+20)*(t-1) = 400
vt=400 =>v=400/t
Thus, you can solve for t.
Followup: But the solution t still includes another variable v? So you can not find a finite answer for t, the answer for t will always include the unknow variable v, wont it?
Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Quantitative Questions Forum
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28 Jan 2009, 12:34
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Here is another way to elaborate the solution.
Actual scenario -
Let r be the rate, t be the time and d be the distance covered.
Given that distand d = 400.
By Rate forumyla, rt = d ==> rt = 400 -----> Eq 1
Hypothetical scenario -
if rate is 20 more than the actual rate, then new rate will be r + 20.
and time will be 1 hr less the actual time, then new time will be t - 1.
Distance is the same = 400.
By Rate forumyla, rate * time = distance, we have (r+20)(t-1) = 400. ---> Eq 2.
We have two unknowns r and t and two eq. Try solving the two equations to get the unknown values.
From eq1, rt= 400 ==> r = 400/t------->Eq 1a derived from Eq 1.
Substitute r from eq 1a in eq 2.
(400/t +20) (t-1) = 400.
Try soving for t from the above eq, and you should be getting the value of t as 5.
Question is asking for the actual time and hence our ans will be 5.
Hope this is clear.
Actual scenario -
Let r be the rate, t be the time and d be the distance covered.
Given that distand d = 400.
By Rate forumyla, rt = d ==> rt = 400 -----> Eq 1
Hypothetical scenario -
if rate is 20 more than the actual rate, then new rate will be r + 20.
and time will be 1 hr less the actual time, then new time will be t - 1.
Distance is the same = 400.
By Rate forumyla, rate * time = distance, we have (r+20)(t-1) = 400. ---> Eq 2.
We have two unknowns r and t and two eq. Try solving the two equations to get the unknown values.
From eq1, rt= 400 ==> r = 400/t------->Eq 1a derived from Eq 1.
Substitute r from eq 1a in eq 2.
(400/t +20) (t-1) = 400.
Try soving for t from the above eq, and you should be getting the value of t as 5.
Question is asking for the actual time and hence our ans will be 5.
Hope this is clear.
Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Quantitative Questions Forum
Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
