Question: With an average speed of 40 Km/h, a train reaches its destination on time. If it goes with an average speed of 35 Km/h, it reaches late by 15 minutes. What is the length of the journey ?

(A) 30 Km
(B) 40 Km
(C) 70 Km
(D) 80 Km
(E) 90 Km

Approach Solution : 1

Let x km be the distance traveled and t hours be the travel time.

A train arrives at its destination on time when traveling at an average speed of 40 km/h.
And so 40t = x
If it travels at a 35 km/h average speed, it will be 15 minutes late.
So, 35(t+15/60) = x
x = 40t = 35(t+1/4)
5t = 35/4t
t = 7/4 hours
x = 40*7/4 = 70 km

Correct Answer: (C)

Approach Solution : 2

For a given distance, speed is inversely proportional to time.

From 40 km/hr, the speed drops to 35 (7/8). As a result, the time will be 8/7, which is the inverse of that.
The time difference is specified as 15 minutes.
The time has increased by one unit in relation to the previously mentioned fraction (8-7).
15 minutes are equal to this one unit.
And so 8 units will therefore take 120 minutes, or 2 hours.
Speed was 35 km/hr when the time was 8 units.
Distance is therefore 35*2 = 70 km.

Correct Answer: (C)

Approach Solution : 3

Average speed = (Total distance traveled) / (total time taken)
Let us consider distance = d kilometer
and time = T hr
Therefore, d/T = 40
=> d/(T+0.25) = 35 (15 minutes can also be said as 0.25 hr)
After resolving the equations, d = 70 km

Correct Answer: (C)

“With an average speed of 40 Km/h, a train reaches its destination on” - is a subject covered in the GMAT quantitative reasoning section. A student needs to be knowledgeable in a wide range of qualitative skills in order to successfully complete GMAT Problem Solving questions. There are 31 questions in the GMAT Quant section overall. Calculative mathematical problems must be solved in the GMAT quant topics' problem-solving section using appropriate mathematical skills.

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