Tom is travelling from city A to city B to city C. From city A to city

Question

Tom is travelling from city A to city B to city C. From city A to city B, he travelled at the rate of 160 km per hour, and from city A to city B, he travelled the distance that is twice of the distance he travelled from city B to city C. What is the average speed rate from city A to city C in total?

(1) Tom travelled from city B to city C at the rate of 100 km per hour.
(2) The total distance from city A to city C is 600 km.

(1) Tom travelled from city B to city C at the rate of 100 km per hour.
(2) The total distance from city A to city C is 600 km.

GMATWhizTeam · Answer

Solution 
 Step 1: Analyse Question Stem 
 • Let’s draw D-S-T table. 
 https://www.dropbox.com/s/w2tnf8aidar8ich/16.jpg?dl=1 
We need to find the average speed from A-C
 •  \frac{240*s}{(1+s)} , we need to find the value of s. 
 Step 2: Analyse Statements Independently (And eliminate options) – AD/BCE 
 Statement 1:  Tom travelled from city B-C at the rate of  100 km/h 
 • This is nothing but the value of  s  only,
• We can find the average speed from A-C 
Hence, statement 1 is sufficient, we can eliminate answer options B, C, and E.
 Statement 2:  Total distance from city A to C is  600  KM.
 • We cannot infer anything about the value of  s .
 o We cannot find the average speed from A-C  
Hence, statement 2 is not sufficient, the correct answer is  Option A.

HarryStamper · Answer

Hi  Bunuel  - do we assume that Tom is not stopping in between or at City B?

As the OA is A, we are making this assumption. But shouldn't the question make this clear?

gurmukh · Answer

In GMAT sums or general in these types of cases we don't assume he might have stopped at B until it is mentioned in the sums. It is just like when we write 1 we know it is positive 1 and not negative 1.

Posted from my mobile device

Franchise · Answer

How come we do not need to know the distance between A and B and B and C in order to find the average speed? Isn't the formula for average speed: Total Distance/Total Time?

Thank you.

elliot12 · Answer

You can use 2x (A -> B) and x (B -> C) to represent the distance traveled, we are given the ratio of distances in the stem.

Logo · Answer

A is sufficient because when you calculate time you will have x incorporated. Therefore, when you calculate total distance over total time, x will cancel out leaving you with an avg rate.

rounakkedia172 · Answer

A-----------------B----------------C
Speed 160km/h..............x
Distance 2d....................d

Average Speed = Total Distance/ Total time taken
 = (2d+d)/   
(Note: why 2d/160 and d/x? We know time = distance/speed, So the respective time taken would be = 2d/160 from A-B and d/x from B to C)
 = 480x/(2x+160). (d gets cancelled out).
So we need the value of x, the speed from B-C, so only Statement 1 is sufficient.

dbcoupie123 · Answer

are we sure A is correct?

the average speed from one point to another is the (distance between the two points) divided by (the total time it took to travel the two points).

In no mention in the question does it say that A to B to C is linear. For all we know, A - B - C can form a triangle.

In order to determine the avg speed from A to C, we need to know the shortest distance between A and C and the total time it took to get from A to C (this includes the time Tom travelled from A to B and B to C).

Had the question asked "what is the average speed of the  total  trip", then we could have used to distance of 3d to determine the average speed of the trip.

Answer should be  C  - 1 & 2 together sufficient

JeffTargetTestPrep · Answer

From A to B:

rate = 160, distance = 2d, and time = distance/rate = 2d/160

From B to C:

rate = x, distance = d, and time = d/x

Since average speed = total distance/total time, we need to answer the question:

average speed = (2d +d)/(2d/160 + d/x) = ?

Statement One Alone:

=> Tom travelled from city B to city C at the rate of 100 km per hour.

x = 100

average speed = (3d)/(2d/160 + d/100) = 3/(2/160 + 1/100)

Statement one is sufficient. Eliminate answer choices B, C, and E.

Statement Two Alone:

=> The total distance from city A to city C is 600 km.

3d = 600

d = 200

average speed = (600)/(400/160 + 200/x)

Clearly, we can’t determine the average speed. Statement two is not sufficient.

Answer: A

Tom is travelling from city A to city B to city C. From city A to city

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Tom is travelling from city A to city B to city C. From city A to city

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