From the area, you can get radius and from that you can get Circumference "C"
This question now boils down to cars A and B which are "C"miles apart, traveling towards each other at speeds of X and Y respectively. How long will they take to meet??
Approx 75mins?
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Car A and Car B
Source: Beat The GMAT — Problem Solving |
Unless I missed some way to simplify the math, this problem isn't very GMATy. First need to take sqrt(1256/pi) to get the radius. You can guesstimate to around 20. Then need the circumference which involves multiplying by pi and then dividing the distance by the rate. I get 75 as well, but again, I don't see how to avoid doing calculations using a numerical estimation of pi
Radius = sqrt(A/pi) = sqrt(1256/3.14) =sqrt(400) = 20
Circumference = 40*pi = 125.6
Car A is going to have to travel 40% of the way round and car B 60% of the way.
Car A travels: 40% of 125.6 = 12.56 x 4 = 50.24 miles
Time = D/S = 50.24/40 = 1.256 hours = 75mins (approx)
Circumference = 40*pi = 125.6
Car A is going to have to travel 40% of the way round and car B 60% of the way.
Car A travels: 40% of 125.6 = 12.56 x 4 = 50.24 miles
Time = D/S = 50.24/40 = 1.256 hours = 75mins (approx)
I think that's what makes the difference in the real exam. A tough question will be tedious to answer (not necessarily always) & someone who is very good (caliber of above 720) will quickly do a comfortable approximation & arrive at the answer, while someone like me would sit calculating each component, spend a lot of energy & get bogged down by the ticking time :roll:cm47323 wrote:Unless I missed some way to simplify the math, this problem isn't very GMATy. First need to take sqrt(1256/pi) to get the radius. You can guesstimate to around 20. Then need the circumference which involves multiplying by pi and then dividing the distance by the rate. I get 75 as well, but again, I don't see how to avoid doing calculations using a numerical estimation of pi
This question is from 800score.com . While their questions park is good, the questions are not very gmat-like. I'vefound many hard questions in gmatprep and gmatfocus, but they simply aren't this difficult or "weird" 
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This question is not at all GMAT like, as has already been noted.
When the direction of a moving body changes it cannot have uniform speed. Constantly varying speeds involve a concept called accelaration, which the GMAT DOES NOT COVER.
Can this be done, assuming speed is a scalar quantity...sure...but it's not very accurate.
When the direction of a moving body changes it cannot have uniform speed. Constantly varying speeds involve a concept called accelaration, which the GMAT DOES NOT COVER.
Can this be done, assuming speed is a scalar quantity...sure...but it's not very accurate.
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One can use relative speed to cut down further on calculations here.
R= sqrt(A/pi) = sqrt(1256/3.14) =sqrt(400) = 20
Time taken(in min.) = (Total Distance / Total relative speed ) *60
= ((2*3.14*20)/100)* 60 = 75 (approx)
Relative speed will be the sum of A & B as they are moving towards each other.
Cheers
R= sqrt(A/pi) = sqrt(1256/3.14) =sqrt(400) = 20
Time taken(in min.) = (Total Distance / Total relative speed ) *60
= ((2*3.14*20)/100)* 60 = 75 (approx)
Relative speed will be the sum of A & B as they are moving towards each other.
Cheers
Last edited by anshulseth on Tue Apr 07, 2009 9:41 am, edited 1 time in total.
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I am positive it was a typo anshuleth.anshulseth wrote:One can use relative speed to cut down further on calculations here.
R= sqrt(A/pi) = sqrt(1256/3.14) =sqrt(400) = 20
Time taken(in min.) = (Total Distance / Total relative speed ) *60
= ((2*3.14*20)/100)* 60 = 75 (approx)
Relative speed will be the sum of A & B as they are moving in the same dir.
Cheers
If using Relative Speeds:
a) Bodies moving in Same direction (Subtract speeds for resultant effective speed)
b) Bodies moving in Opposite direction (Add speeds for resultant effective speed)
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@Musiq
I am right and u are also right.
Now, how do u explain that.
I meant relative speed adds when objects move towards each other,
and u say that they add when they move in opposite direction.
Which is one and the same here, clockwise and anti-clockwise..
Got it.. :roll:
Though i must correct my post to say, that they are moving towards each other.
I am right and u are also right.
Now, how do u explain that.
I meant relative speed adds when objects move towards each other,
and u say that they add when they move in opposite direction.
Which is one and the same here, clockwise and anti-clockwise..
Got it.. :roll:
Though i must correct my post to say, that they are moving towards each other.
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