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

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

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.


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


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.

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

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

(1) Distance = 500kms, Time = 20/3hrs, average speed = 75kmph. Sufficient.

(2) Y_time = 500/100 = 5hrs, X_time = 5+5/3 = 20/3hrs, X_distance = 500, therefore, X_speed =75kmph. Sufficient.

Hence, option D.