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# Car X and car Y ran a 500-kilometer race. What was the average speed

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Car X and car Y ran a 500-kilometer race. What was the average speed  [#permalink]

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07 Nov 2018, 09:52
1
3
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Difficulty:

15% (low)

Question Stats:

73% (00:57) correct 27% (01:02) wrong based on 343 sessions

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Project DS Butler: Day 2: Data Sufficiency (DS3)

Car X and car Y ran a 500-kilometer race. What was the average speed of car X?

(1) Car X completed the race in 6 hours and 40 minutes.
(2) Car Y, at an average speed of 100 kilometers per hour, completed the race I hour and 40 minutes before car X crossed the finish line.

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Re: Car X and car Y ran a 500-kilometer race. What was the average speed  [#permalink]

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07 Nov 2018, 10:37
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1
Distance is given. Dist for X = Dist for Y = 500km.

Stmt 1: Time for X is given. So Avg Speed can be calculated. Hence Sufficient.

Stmt 2: Avg Speed for Y is given, so Time for Y = Dist for Y/Avg Speed for Y = 500/100 = 5 hrs. Now, it is given that X took 1 hour and 40 minutes more. So, Time for X = 6 hours 40 min, distance for X is known, again, average speed can be calculated. Hence Sufficient.

Hence Option D
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Re: Car X and car Y ran a 500-kilometer race. What was the average speed  [#permalink]

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07 Nov 2018, 11:47
gmatbusters wrote:
Car X and car Y ran a 500-kilometer race. What was the average speed of car X?
(l) Car X completed the race in 6 hours and 40 minutes.
(2) Car Y, at an average speed of 100 kilometers per hour, completed the race I hour and 40 minutes before car X crossed the finish line.

To practice DS daily practice problems, follow DS Butler

Average Speed = Distance / Time

Total Distance = 500

Statement 1: Time is mentioned . So we can calculate the speed. Sufficient.

Statement 2: comparative rate is given. Y needs 5 hours as y runs at a speed of 100 km and y has finished the race 1 hour and 40 minutes before the x finished the race. So X needs total 6 hours and 40 minutes. So we can figure out the speed. Sufficient.

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Re: Car X and car Y ran a 500-kilometer race. What was the average speed  [#permalink]

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08 Nov 2018, 09:11
Data: Distance = Given, Speed of Car X = to find out (Speed = Dist / Time)

Statement 1: Time given. Speed can easily be calculated .... Sufficient
Statement 2: Speed of Car Y given, time taken by Car 2 can be calculated with above Speed equation. Now time taken by Car Y minus 1 hr 40 mint = time taken by Car X. So once we have time taken by Car X, we can easily calculate its Speed... Sufficient

So both statements alone are sufficient .... Answer = D

Note: These type of questions should be answered without actually calculating/finding out a numeric value for Speed
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Re: Car X and car Y ran a 500-kilometer race. What was the average speed  [#permalink]

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08 Nov 2018, 21:22
Quote:
Car X and car Y ran a 500-kilometer race. What was the average speed of car X?

One of the efficient ways to solve work and distance problem is to prepare a table as
shown (use mnemonic : DIRT and ART , where distance = rate * time ; amount of work done = rate of work * time
for recalling under stressed condition )

Average speed = total distance / total time
Given from Q stem: distance travelled by X.
So if we know total time taken by X for cover 500 km, we can get an unique answer to the question.

Quote:
(1) Car X completed the race in 6 hours and 40 minutes.

Directly total travel time is given, so average speed can be known. Sufficient.

Quote:
(2) Car Y, at an average speed of 100 kilometers per hour, completed the race I hour and 40 minutes before car X crossed the finish line.

We can calculate time taken by Y from table and then calculate time taken by X since a linear relationship of difference
between time taken by X and Y each is known from St 2. Suff.
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Re: Car X and car Y ran a 500-kilometer race. What was the average speed  [#permalink]

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09 Nov 2018, 23:26
1
gmatbusters wrote:

Project DS Butler: Day 2: Data Sufficiency (DS1)

Car X and car Y ran a 500-kilometer race. What was the average speed of car X?

(1) Car X completed the race in 6 hours and 40 minutes.
(2) Car Y, at an average speed of 100 kilometers per hour, completed the race I hour and 40 minutes before car X crossed the finish line.

For calculating average speed, we need to use the formula:

$$Average-Speed=\frac{(Total-Distance-Covered)}{(Total-Time-Taken)}$$

We know the total distance is 500 Km. All we need is total time taken by X.

Statement 1: We are given the total time taken by X. Hence this is SUFFICIENT

Statement 2: Car y completes the lace in 500/100 hours i.e 5 hours. Hence Car X completes in 5 hour + 1 hour 40 minutes = 6 hour 40 minutes. Hence this too is SUFFICIENT

Hence, the correct answer is D
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Re: Car X and car Y ran a 500-kilometer race. What was the average speed  [#permalink]

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09 Nov 2018, 23:58
To calculate average speed, we need Total Distance and Total Time.

(1) Car X completed the race in 6 hours and 40 minutes.
We have total distance, 500, and total time, 6 hours and 40 minutes. We can calculate the Average speed
SUFFICIENT

(2) Car Y, at an average speed of 100 kilometers per hour, completed the race 1 hour and 40 minutes before car X crossed the finish line.
We can calculate the total time it took car Y to complete the race, 5 hours and add 1 hour and 40 minutes to that to get the total time it took for car X to finish the race.
SUFFICIENT

Hence, D
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Re: Car X and car Y ran a 500-kilometer race. What was the average speed  [#permalink]

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24 Nov 2019, 06:29
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Re: Car X and car Y ran a 500-kilometer race. What was the average speed   [#permalink] 24 Nov 2019, 06:29
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