Speed, Time and Distance

It is an important topic and includes relationship between speed, time, distance. Different units of measurement of these quantities. Also included are concepts on average speed and relative speed. 4GMAT's GMAT Math Lesson Book in this chapter covers the following concepts:

1. The meaning of distance, time and speed has been given and their respective units of measurement have also been given.
2. The relationship between the three has also been highlighted and for the better understanding of the concept illustrative examples have been provided.
3. Simple conversion factors for different units of speed, time and distance such as conversion between mph to kmph or m/sec.
4. Method to calculate average speed under three different circumstances has been explained along with examples
5. Definition of the term relative speed and the method of calculation when traveling in the same direction and different directions are explained
6. 23 solved examples of the above mentioned concepts are given with detailed explanation and the short cuts that can be used to arrive at the result quicker have been mentioned wherever applicable
7. In addition, boats in streams (Upstream and downstream) have been explained and to aid the understanding process solved examples have also been worked out
8. 24 exercise problems have been asked and the answer to the questions has also been provided along with explanatory answers
9. An objective type speed test with around 40 questions with explanatory answers and answer key provided for the speed test

Here is an example of a typical solved example in this chapter.
Sample Question
Question
A boat travels upstream at a speed of 30 mph and then downstream at a speed of 45 mph. What is the speed of the boat in still water and what is the speed of the stream?

Explanatory Answer
When the downstream speed (D) and upstream (U) of a boat are given:
The speed of boat in still water, B = (D + U) / 2 = (45 + 30) / 2 = 37.5 mph
Speed of the stream S = ((D - U) / 2) = ((45 - 30) / 2) = 7.5 mph