Basic formulas:
Distance= Speed x Time
Conversion:
1. (km/h) x 5/18 = m/s
2. (m/s) x 18/5 = km/h
3. 1 mile = 1.61 kilometer
BASIC CONCEPT:
Average speed:
If the distance remains the same for two scenarios (going to a place & returning), to find the average speed from a given speed, follow this formula:
S= (2S1S2)/(S1+S2)
Here,
S1= speed of going somewhere
S2= speed of returning
AVERAGE SPEED:
For boat related problems:
Use the following formula:
1. B+C=D
2. B-C=U
3. B= (D+U)/2
4. C= (D-U)/2
5. D=U + (2x C)
Here,
B= Speed of the boat in still water
U= Upstream
D= Downstream
C= Speed of current
Video on “Boat Related Problems”:
Relative speed:
1. If two objects are going in the same direction, the relative speed is the difference in their speed.
2. If two objects approach from the opposite directions, the relative speed is the sum of their speed.
Video on “Relative Speed”:
Train problems:
S1 ± S2 = (l1 + l2)/t
Here,
S1= Speed of train 1
S2 = Speed of Train 2/ Human/ Bridge/ Post [For bridge and post, S2= 0]
I1= length of train 1
l2= length of train 2/ human/bridge/ post [for human and post, I2= 0]
t= total time taken
Catching or meeting problems:
1. To find time to catch another object,
Catching time = Distance already traveled by the object that started earlier / Difference of their speed
2. To find time to meet two objects,
Meeting time = Distance yet to be traveled / Sum of their speed
Video on “Speed, Distance, Time”:
To know more about this topic, go to the below link:
GMAT Club - Speed Distance & Time