Concept of Quantitative Aptitude: Time and Distance
1 hour = 60 min = 360 seconds
1 km = 1000 m
1 mile = 1.60 km [SI unit of speed is m/s]
- Suppose while travelling a certain distance 'd' if there is a change in speed in the ratio m:n ,
then the ratio of time taken will become n: m.
- If speed changes during the journey then average speed will be = 2xy/x+y
- When objects move in the same direction with speed S1 and S2 resp.
Then relative speed = S1 – S2
- When an object moving in the opposite direction with speed S1 and S2 resp.
Then their Relative speed will be = S1 + S2
- When objects move towards each other.
Then time taken by them to meet will be = Distance/S1+S2
- When an object moving in the opposite direction time taken to meet will be = Distance/S1-S2
To make it understand have a look into some examples -
1. Two trains X and Y of lengths 450 meters and 550 meters, respectively, are running in the same direction on parallel tracks. If the speeds of X and Y are 58 km/h and 86 km/h, respectively, then what will be the time taken by them to cross each other? (correct to one decimal place)
A. 128.6 seconds
B. 122.6 seconds
C. 124.6 seconds
D. 126.6 seconds
2. If a person walks at 14 km/hr instead of 12 km/hr, he would have walked 1 km more in the same time. What is the actual distance (in kms) travelled by him at 12 km/hr in the same time?
3. Two trains start at the same time from two stations and proceed towards each other at speeds of 90 km/h and 70 km/h, respectively. When they meet, it is found that one train has travelled 140 km more than the other. What is the distance in km) between the two stations?
Solution 1: Answer (A)
Solution 2: Answer (C)
Solution 3: Answer (B)
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