Speed Time Distance Questions - Average Speed and Rule of Alligation : Ascent - CAT Correspondence Course

Question 4 the day : June 5, 2003
The question for the day is from the topic Speed, Time and Distance. The question helps understand concepts related to average speed and how it can be used in conjunction with the rule of alligation.

Question
I travel the first part of my journey at 40 kmph and the second part at 60 kmph and cover the total distance of 240 km to my destination in 5 hours. How long did the first part of my journey last?

1. 4 hours
2. 2 hours
3. 3 hours
4. 2 hours 24 minutes

Correct Answer is 3 hours. Choice (3) is right.

Explanatory Answer

The total time of journey = 5 hours.
Let 'x' hours be the time that I traveled at 40 kmph
Therefore, 5 - x hours would be time that I traveled at 60 kmph.

Hence, I would have covered x*40 + (5 - x)60 kms in the 5 hours = 240 kms.

Solving, for x in the equation 40x + (5 - x)*60 = 240, we get
40x + 300 - 60x = 240

=> 20x = 60 or x = 3 hours.

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