M08: q02

Question

If it took a bus three hours to get from town A to town B, what was the average speed of the bus for the entire trip?

1. During the first hour the bus finished  \frac{1}{3}  of the distance going 60 kmh.
 2. During the second hour the average speed of the bus was 120 kmh, twice its speed during the third hour.

OA - 
 Statement (1) by itself is sufficient. From S1  \frac{1}{3}  of the distance amounts to 60 km. Therefore, the entire distance is 180 km and the average speed for the entire trip is  \frac{180 km}{3 h} = 60 kmh  .  how do we know that tha bus continued at the same speed for the rest of the two hours....? in GMAT questions, S1 and S2 must not clash and according to this one the bus travelled at 60km during the second hour but according to S2 it travelled at 120.....
please explain OR rephrase the question

Statement (2) by itself is insufficient. S2 gives no information about the first hour.
The correct answer is A.

mads · Answer

From the question atem, we know that total time t = 3 hours.
We need to know total distance so that the average speed can be calculated. Avg Speed = Total Distance/Total time.

Statement1: In 1 hour bus has travelled 1/3 distance with 60 km per hour. It have travelled 60 km in that hour and it is 1/3 of the distance. So the total distance is 60*3 = 180 km.
Now we know total distance, avg speed = total distance/ total time => 180/3
Sufficient.

Next step is to check if statement 2 alone is sufficient.
Statement2: This statement gave the average speed for 2nd hour and 3rd hour. But we dont know the average speed in 1st hour. If we knew first hour avg speed, then we could have concluded on the total distance travelled and then the qaverage speed.
So This is not Sufficient to answer the question.

Hope this helps.

nishtil · Answer

IMO the two statements are contradicting.

Statement 1: The total distance travel is 180. The distance travel in first hr is 60.
statement 2: The distance travel in second Hr is 120. and distance in third Hr is 60.

Combining two statement : total distance travel is 240. However, the distance as per statement 1 is 180.

Isn't the two statement contradicts.

Please advice weather my thinking is correct

Bunuel · Answer

Revised version of this question is below:

If it took a bus three hours to get from town A to town B, what was the average speed of the bus for the entire trip?

Average \ speed=\frac{total \ distance}{total \ time} , we know that total time is 3 hours, so we need to find the total distance.

(1) During the first hour the bus finished  \frac{1}{3}  of the distance at an average speed of 60 kilometers per hour -->  \frac{1}{3}  of the distance is 1*60=60 kilometers, hence the total distance is 3*60=180 kilometers. Sufficient.

(2) During the second hour the average speed of the bus was 80 kilometers per hour, twice its speed during the third hour. During the second hour the bus covered 80 kilometers and during the third hour the bus covered 80/2=40 kilometers, so during the last two hours it covered total of 120 kilometers. We don't know how many kilometers were covered during the first hour, hence this statement is not sufficient.

Answer: A.

M08: q02

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