Races: A race is a contest of speed in running, riding, driving, sailing or rowing.
Race course: A race course is the ground or path on which contests are made.
Starting point: A starting point is the point from which a race begins.
Winning point: Winning point is the point set to bound a race. It is also known as goal.
Winner: Winner is the first person who reaches the winning goal.
Dead heat race: Dead heat race is defined as the race in which all the persons contesting a race reach the goal exactly at the same time.
Start: If before the start of the race, A is at the starting point and B is ahead of A by 12 meters, then 'A gives B, a start of 12 meters'.
Here, A and B are two contestants in a race.
Example: To cover a race of 100 meters in this case, A will have to cover 100 meters while B will have to cover only (100 - 12) = 88 meters.
In a 100 meters race, 'A can give 12 meters' or 'A can give B a start of 12 meters' or 'A beats B by 12 meters' means that while A runs 100 meters, B runs (100 - 12) = 88 meters.
Games: 'A game of 100, means that the person among the contestants who scores 100 points first is the winner'.
If A scores 100 points while B scores only 80 points, then 'A can give B 20 points'.
Concept 1:
In a game of 100 points, A can give B 20 points and C 28 points. How many points can B give C?
Example 1:
In a game of 100 points, A can give B 20 points and C 28 points. How many points can B give C?
Solution:
By the time A scores 100 points, B scores only 80 and C scores only 72 points.
Let the Scoring Rate of A be Sa. (Scoring Rate = [latex]\frac{score}{time}[/latex])
Scoring Rate of B, Sb = [latex]\frac{80}{100}[/latex] x Sa = 0.8 Sa
Scoring Rate of C, Sc = [latex]\frac{72}{100}[/latex] x Sa = 0.72 Sa
Time taken for B to get 100 points = [latex]\frac{100}{sb}[/latex] = [latex]\frac{100}{(0.8 \times Sa)}[/latex]
Score taken by C in this time period = Sc x [latex]\frac{100}{(0.8 \times Sa)}[/latex] = [latex]\frac{72}{0.8}[/latex] = 90
Thus, B can give C 10 points.
Example 2:
In a 200 m race A beats B by 35 m or 7 sec. Find A's time over the course.
Solution:
By the time A completes the race, B is 35m behind A and would take 7 more seconds to complete the race.
=> B can run 35 m in 7 s. Thus, B’s speed = [latex]\frac{35}{7}[/latex] = 5 m/s.
Time taken by B to finish the race = [latex]\frac{200}{5}[/latex] = 40 s.
Thus, A’s time over the course = (40 – 7)s = 33 s.
Concept 2:
If A runs x times faster than B, A’s speed is actually 1+x the speed of B
Example 1:
A runs [latex]1\frac{2}{3}[/latex] times as fast as B. If A gives B a start of 80 m, how far must the winning post be so that A and B might reach it at the same time?
Solution:
Speed of A, Sa = [latex]\frac{5}{3}[/latex] x Sb
Let the distance of the course be ‘d’ meters
Time taken by A to cover distance ‘d’ = Time taken by B to cover distance‘d-80’
[latex]\frac{d}{[\frac{5}{3} \times Sb]}[/latex] = [latex]\frac{(d - 80)}{Sb}[/latex]
3d = 5d – 400
=> 2d = 640 => d = 200m
Example 2:
A runs [latex]1\frac{2}{3}[/latex] times faster than B. If A gives B a start of 80 m, how far must the winning post be so that A and B might reach it at the same time?
Solution:
Speed of A, Sa = (1 + [latex]\frac{5}{3}[/latex]) x Sb = [latex]\frac{8}{3}[/latex] x Sb
Let the distance of the course be ‘d’ meters
Time taken by A to cover distance ‘d’ = Time taken by B to cover distance ‘d-80’
[latex]\frac{d}{[\frac{8}{3} \times Sb]}[/latex] = [latex]\frac{(d - 80)}{Sb}[/latex]
3d = 8d – 640
=> 5d = 640 => d = 128m