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18 Jul 2024, 07:00
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E
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Difficulty:
65%
(hard)
Question Stats:
58% (02:04) correct
42%
(02:20)
wrong
based on 333
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Train A and Train B each departed simultaneously from Liverpool heading to London, which is 300 kilometers away. When Train A reached the destination, Train B still had 80 kilometers left to cover. What was Train A's average speed during this journey?
(1) During the first hour, Train B covered 40 kilometers less than Train A.
(2) Train B's average speed for the first 110 kilometers was 110 kilometers per hour.
A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient to answer the question asked.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient to answer the question asked.
C. BOTH statements (1) and (2) TOGETHER are sufficient to answer the question asked, but NEITHER statement ALONE is sufficient to answer the question asked.
D. EACH statement ALONE is sufficient to answer the question asked.
E. Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed.
(1) During the first hour, Train B covered 40 kilometers less than Train A.
(2) Train B's average speed for the first 110 kilometers was 110 kilometers per hour.
A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient to answer the question asked.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient to answer the question asked.
C. BOTH statements (1) and (2) TOGETHER are sufficient to answer the question asked, but NEITHER statement ALONE is sufficient to answer the question asked.
D. EACH statement ALONE is sufficient to answer the question asked.
E. Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed.
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18 Jul 2024, 08:00
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Train A and Train B each departed simultaneously from Liverpool heading to London, which is 300 kilometers away. When Train A reached the destination, Train B still had 80 kilometers left to cover. What was Train A's average speed during this journey?
Essentially, we are given that Train A covered 300 kilometers in the same time Train B covered 220 kilometers and are asked to find the average speed of Train A during this 300-kilometer trip.
(1) During the first hour, Train B covered 40 kilometers less than Train A.
Don't fall into the trap of assuming the trains maintained the same constant speed throughout their journey. If that were true, then we could reason that in the first hour, Train B fell behind by 40 kilometers. Therefore, to fall behind by 80 kilometers, it would need 2 hours, which would mean that Train A covered 300 kilometers in 2 hours, making its average speed equal to 300/2 = 150 kilometers per hour. However, this would not be correct because we cannot assume constant speed. It's possible, for example, that in the first hour, Train B covered 110 kilometers and Train A covered 150 kilometers. After that, they could have slowed down, and Train A could have covered the remaining 150 kilometers in 2 hours, spending a total of 3 hours on the journey and making its average speed equal to 300/3 = 100 kilometers per hour. Not sufficient.
(2) Train B's average speed for the first 110 kilometers was 110 kilometers per hour.
Again, don't fall into the trap of assuming the trains maintained the same constant speed throughout their journey. If that were true, then we could reason that Train B covered 220 kilometers in 2 hours, which would mean that Train A covered 300 kilometers in 2 hours, making its average speed equal to 300/2 = 150 kilometers per hour. However, this would not be correct because we cannot assume constant speed. It's possible, for example, that in the first hour, Train B covered 110 kilometers and Train A covered 150 kilometers. After that, they could have slowed down, and Train A could have covered the remaining 150 kilometers in 2 hours, spending a total of 3 hours on the journey and making its average speed equal to 300/3 = 100 kilometers per hour. Therefore, Statement 2 is not sufficient.
(1) + (2) We can use the same example as above: the average speed of Train A can be 150 kilometers per hour, assuming constant speeds for both trains, or some other speed, for example, 100 kilometers per hour if in the first hour Train B covered 110 kilometers and Train A covered 150 kilometers, and after that they slowed down and Train A covered the remaining 150 kilometers in 2 hours, spending a total of 3 hours on the journey and making its average speed equal to 300/3 = 100 kilometers per hour. Therefore, even together, the statements are not sufficient.
Answer: E.
GMAT Club Official Explanation:
Train A and Train B each departed simultaneously from Liverpool heading to London, which is 300 kilometers away. When Train A reached the destination, Train B still had 80 kilometers left to cover. What was Train A's average speed during this journey?
Essentially, we are given that Train A covered 300 kilometers in the same time Train B covered 220 kilometers and are asked to find the average speed of Train A during this 300-kilometer trip.
(1) During the first hour, Train B covered 40 kilometers less than Train A.
Don't fall into the trap of assuming the trains maintained the same constant speed throughout their journey. If that were true, then we could reason that in the first hour, Train B fell behind by 40 kilometers. Therefore, to fall behind by 80 kilometers, it would need 2 hours, which would mean that Train A covered 300 kilometers in 2 hours, making its average speed equal to 300/2 = 150 kilometers per hour. However, this would not be correct because we cannot assume constant speed. It's possible, for example, that in the first hour, Train B covered 110 kilometers and Train A covered 150 kilometers. After that, they could have slowed down, and Train A could have covered the remaining 150 kilometers in 2 hours, spending a total of 3 hours on the journey and making its average speed equal to 300/3 = 100 kilometers per hour. Not sufficient.
(2) Train B's average speed for the first 110 kilometers was 110 kilometers per hour.
Again, don't fall into the trap of assuming the trains maintained the same constant speed throughout their journey. If that were true, then we could reason that Train B covered 220 kilometers in 2 hours, which would mean that Train A covered 300 kilometers in 2 hours, making its average speed equal to 300/2 = 150 kilometers per hour. However, this would not be correct because we cannot assume constant speed. It's possible, for example, that in the first hour, Train B covered 110 kilometers and Train A covered 150 kilometers. After that, they could have slowed down, and Train A could have covered the remaining 150 kilometers in 2 hours, spending a total of 3 hours on the journey and making its average speed equal to 300/3 = 100 kilometers per hour. Therefore, Statement 2 is not sufficient.
(1) + (2) We can use the same example as above: the average speed of Train A can be 150 kilometers per hour, assuming constant speeds for both trains, or some other speed, for example, 100 kilometers per hour if in the first hour Train B covered 110 kilometers and Train A covered 150 kilometers, and after that they slowed down and Train A covered the remaining 150 kilometers in 2 hours, spending a total of 3 hours on the journey and making its average speed equal to 300/3 = 100 kilometers per hour. Therefore, even together, the statements are not sufficient.
Answer: E.
General Discussion
18 Jul 2024, 07:37
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Given: Train A and Train B each departed simultaneously from Liverpool heading to London, which is 300 kilometers away. When Train A reached the destination, Train B still had 80 kilometers left to cover.
Asked: What was Train A's average speed during this journey?
Train A
Distance = 300 km
Let Average Speed = x km/hr
Time Required = 300/x hrs
Train B
Distance = 300 - 80 = 220 km
Time taken = 300/x hrs
Average Speed = 220/(300/x) = 11x/15 km/hr
(1) During the first hour, Train B covered 40 kilometers less than Train A.
During the first hours, Train B covered distance less than A = x - (11x/15) = 4x/15 = 40
x = 40*15/4 = 150 km/hrs
Train A's average speed during this journey = x = 150 km/hr
SUFFICIENT
(2) Train B's average speed for the first 110 kilometers was 110 kilometers per hour.
Since it is NOT mentioned that trains were moving at constant speeds.
Train B's avereage speed for total 220 km can not be ascertained which is 11x/15 km/hr
Therefore, Train A's average speed during this journey can not be derived.
NOT SUFFICIENT
IMO A
Asked: What was Train A's average speed during this journey?
Train A
Distance = 300 km
Let Average Speed = x km/hr
Time Required = 300/x hrs
Train B
Distance = 300 - 80 = 220 km
Time taken = 300/x hrs
Average Speed = 220/(300/x) = 11x/15 km/hr
(1) During the first hour, Train B covered 40 kilometers less than Train A.
During the first hours, Train B covered distance less than A = x - (11x/15) = 4x/15 = 40
x = 40*15/4 = 150 km/hrs
Train A's average speed during this journey = x = 150 km/hr
SUFFICIENT
(2) Train B's average speed for the first 110 kilometers was 110 kilometers per hour.
Since it is NOT mentioned that trains were moving at constant speeds.
Train B's avereage speed for total 220 km can not be ascertained which is 11x/15 km/hr
Therefore, Train A's average speed during this journey can not be derived.
NOT SUFFICIENT
IMO A
