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word problem

by sud21 » Thu Jan 12, 2012 9:40 am
There is a car and a truck, in the same duration, car traveled 120 miles, and truck traveled 100 miles. What is the average speed of truck in this period?
1) In the first 30 min, car traveled 30 miles.
2) The average speed of the car is 10 miles/hour more than the truck.
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by user123321 » Thu Jan 12, 2012 11:26 am
sud21 wrote:There is a car and a truck, in the same duration, car traveled 120 miles, and truck traveled 100 miles. What is the average speed of truck in this period?
1) In the first 30 min, car traveled 30 miles.
2) The average speed of the car is 10 miles/hour more than the truck.
1) since we dont know car's speed after 30 min. it is difficult to determine car's average speed. so insuff.

2) Cars average speed is 10 miles/hr more than truck. still we cannot determine the truck's average speed. so insuff.

using both, still insuff.
[spoiler]IMO E?[/spoiler]

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by LalaB » Thu Jan 12, 2012 11:34 am
sud21 wrote:There is a car and a truck, in the same duration, car traveled 120 miles, and truck traveled 100 miles. What is the average speed of truck in this period?
1) In the first 30 min, car traveled 30 miles.
2) The average speed of the car is 10 miles/hour more than the truck.
imho A

since time is equal(the same duration is mentioned in the text), from stmnt 1 we can easily find t(time). knowing t, we can find av.speed. av.speed =220/2t

b is insuff, since we do not know either speed, or time
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by chufus » Thu Jan 12, 2012 11:39 am
user123321 wrote:
sud21 wrote:There is a car and a truck, in the same duration, car traveled 120 miles, and truck traveled 100 miles. What is the average speed of truck in this period?
1) In the first 30 min, car traveled 30 miles.
2) The average speed of the car is 10 miles/hour more than the truck.
1) since we dont know car's speed after 30 min. it is difficult to determine car's average speed. so insuff.

2) Cars average speed is 10 miles/hr more than truck. still we cannot determine the truck's average speed. so insuff.

using both, still insuff.
[spoiler]IMO E?[/spoiler]

user123321

I think the answer should be D

Statement A.

Car travels 30 miles in 30 mins
So speed of Car = 60 miles per hour
Car travelled 120 miles
So time taken by Car is 2 hours

In 2 hours truck travels 100 miles so speed of truck is 50 miles/hr . SUFFICIENT

Statement B.

Let speed of truck = x

Speed of Car = x+10

Now the time taken is distance/speed, right?

Time taken for both is same. We know the distance of both. So lets setup the equation:

100/x = 120/x+10

100x + 1000 = 120x
20x = 1000
so x = 50

So speed of truck is 50 miles/ hr. Sufficient

D
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by user123321 » Thu Jan 12, 2012 11:42 am
user123321 wrote:
sud21 wrote:There is a car and a truck, in the same duration, car traveled 120 miles, and truck traveled 100 miles. What is the average speed of truck in this period?
1) In the first 30 min, car traveled 30 miles.
2) The average speed of the car is 10 miles/hour more than the truck.
1) since we dont know car's speed after 30 min. it is difficult to determine car's average speed. so insuff.

2) Cars average speed is 10 miles/hr more than truck. still we cannot determine the truck's average speed. so insuff.

using both, still insuff.
[spoiler]IMO E?[/spoiler]

user123321
I checked in another forum. it should be B.
B) 120/T - 100/T = 10.
you can get T and then from that 120/T. hence suff.

nice problem.

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by chufus » Thu Jan 12, 2012 11:44 am
user123321 wrote:
user123321 wrote:
sud21 wrote:There is a car and a truck, in the same duration, car traveled 120 miles, and truck traveled 100 miles. What is the average speed of truck in this period?
1) In the first 30 min, car traveled 30 miles.
2) The average speed of the car is 10 miles/hour more than the truck.
1) since we dont know car's speed after 30 min. it is difficult to determine car's average speed. so insuff.

2) Cars average speed is 10 miles/hr more than truck. still we cannot determine the truck's average speed. so insuff.

using both, still insuff.
[spoiler]IMO E?[/spoiler]

user123321
I checked in another forum. it should be B.
B) 120/T - 100/T = 10.
you can get T and then from that 120/T. hence suff.

nice problem.

Thanks,
user123321
Dude the answer should be D. The other forum is definitely wrong. See the solution above...
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by LalaB » Thu Jan 12, 2012 11:45 am
@user123321

nope D is ok. stmnt 1 is good enough to find the answer.

p.s. my fault. i misunderstood the q.stem 1st, and thought that we should find the average speed of two cars.
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by user123321 » Thu Jan 12, 2012 12:47 pm
LalaB wrote:@user123321

nope D is ok. stmnt 1 is good enough to find the answer.

p.s. my fault. i misunderstood the q.stem 1st, and thought that we should find the average speed of two cars.
I am sorry, I am still not understanding :(
I think in 1) we just know the speed for first 30 minutes. what after that it got slowed, then its time to travel 120 miles will get increased.
can we assume that car traveled the entire distance with the same speed 60mph?

Thanks,
user123321

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by LalaB » Thu Jan 12, 2012 12:50 pm
@user123321, good point! nowhere is mentioned,that a speed is constant
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by pemdas » Thu Jan 12, 2012 1:07 pm
..looks like this thread has not exhausted the q. solution
car -- t-- 120
truck -- t-- 100
find average speed truck ? average speed truck = 100/t

st(1) implies 90 miles traveled by car took (t-30 minutes) time, and this is Not Sufficient to deduce total time

st(2) average speed car= average speed truck + 10

let's denote average speed car as C and average speed truck as T, then 120/C+10=100/C as C=T+10 :: 120C=100C+1000, C=50 and T=40 Sufficient

b
sud21 wrote:There is a car and a truck, in the same duration, car traveled 120 miles, and truck traveled 100 miles. What is the average speed of truck in this period?
1) In the first 30 min, car traveled 30 miles.
2) The average speed of the car is 10 miles/hour more than the truck.
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by pemdas » Thu Jan 12, 2012 1:12 pm
RTD questions always apply different speed/rate for different portions of distance. It says precisely *In the first 30 min* so fo car it's possible to travel in the next 30 minutes with different speed, all else given this can be even the next 5 or 10 minutes
chufus wrote:
user123321 wrote:
sud21 wrote:There is a car and a truck, in the same duration, car traveled 120 miles, and truck traveled 100 miles. What is the average speed of truck in this period?
1) In the first 30 min, car traveled 30 miles.
2) The average speed of the car is 10 miles/hour more than the truck.
1) since we dont know car's speed after 30 min. it is difficult to determine car's average speed. so insuff.

2) Cars average speed is 10 miles/hr more than truck. still we cannot determine the truck's average speed. so insuff.

using both, still insuff.
[spoiler]IMO E?[/spoiler]

user123321

I think the answer should be D

Statement A.

Car travels 30 miles in 30 mins
So speed of Car = 60 miles per hour
Car travelled 120 miles
So time taken by Car is 2 hours

In 2 hours truck travels 100 miles so speed of truck is 50 miles/hr . SUFFICIENT

Statement B.

Let speed of truck = x

Speed of Car = x+10

Now the time taken is distance/speed, right?

Time taken for both is same. We know the distance of both. So lets setup the equation:

100/x = 120/x+10

100x + 1000 = 120x
20x = 1000
so x = 50

So speed of truck is 50 miles/ hr. Sufficient

D
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