Published on January 16th, 2011 In category Education | Maths

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Solving problems on time, distance and speed

The time, distance and speed problems are the most common type of the problems asked in the competitive examinations, yet many of us make very simple common mistakes. In this post we try to understand this concept and apply a very simple formula for these types of problems. Latter on this post there are some typical type of DST problems and best way to solve these problems.

The formula is Distance = Speed x time

While the formula seems to very simple, there is always a simple logic asked in the questions which is important to be understood. After you have read this concept, you can practice your understanding by trying this quiz.

Also it is important we should note the

Some important Points:   Always pay attention to units some time the units are given in 2 format like miles or Kms. For reference 1 mile = 1.6 Kms

Average Speed :   Most of the problems are given on average speed. This concept has different connotations for the problems in the way it is presented.  For example to drive upto town A that is 100 miles away will take 2 hours if I am travelling at avg. speed of 50 miles per hour. However that does not means I can’t drive mor than 50 miles per hour. I can opt to stop on the way for sometime and drive fast while on the road. The time taken will remain same.  Most of the problem it is safe to assume speed given is average and solve for not available variable.

Travelling in same direction or Overtaking : In case of overtaking, at the time of overtaking the distance travelled by 2 vehicle is same. Use this concept to make the equation with D = S x T and solve the problem

Travelling  in opposite direction (meeting or Collision) :  The distance travelled by both vehicle or objects is sum of initial distance between the vehicle. If starting at same time, the time of travel will be the same.

Running in circle or Circular Car Track problems: The distance travelled is same, this can be easily used in the equations. We will solve the example problems on this types latter on

Problem Types

Multiple speed problem : For problem of type like Shyam drove from Town A to Town B which is at a distance of 100 miles with Avg. speed of  40 km per hr.  A strech of road of 10 miles is under repair and can’t be driven at speed more than 25 miles per hour. What would have been speed of the Shyam in road that was good to drive?    Solution for these types of problem calls for attention like Units Kms, Miles and forming simple equation for parts of the drive will let you solve the problem

Always check the logic first:  For example a problem of this type. To get into semifinal for a race, a runner has to cover the track that is 1 km long with an avg. speed of the 60 kph.  If runner slips on the track  and his average speed while on half way the track is 30 kmph how fast he should run the next half KM so that he qualifies for semifinal.  Solution: If you note the Runner in this case will never qualify.. so you should not waste time WHY?  TO qualify runner has to cover 1 Km in 2 min at 40 Kmph speed, if he is running at 30 kmph for half km he has already used 2 min so will not qualify

As a next part we will cover some common type of problems asked in this topic. Till then enjoy this and let your comments pours in

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