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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