Basic Formula:
Distance = Speed * Time
Average Speed = 2 x y / (x+y) Kmph.
Average Speed = 3 x y z / ( xy + yz+zx) Kmph
TRICK 1: When 2 different speeds are given and total time taken to cover the entire distance is given, then we can find the distance from one side by this formula-
Distance from one end =(Product of two speeds)*(Total time taken)/(Addition of two speeds)
Example :
A girl goes to school with the speed of 6km/hr and returns with the speed of 5 km/hr. If she takes 5.5 hours in all then the distance in km between her house and school is:
Solution- Now, the speeds are 6 km/h and 5 km/h and the total time taken is 5.5 hours.
The distance from college to house can be calculated by putting the values in the formula mentioned above.
Required Distance= (6*5) * 5.5/ (6+5) = 15 kms.
Note : distance for both the speeds being same so entire distance is twice the distance from one side.
TRICK 2: When 2 different speeds are given along with 2 different arrival times, then the distance can be found by
Required Distance = (Product of the speeds)*(Difference between the arrival times) / (Difference of the two speeds)
Example:
A boy covers a certain distance between his college and house on bike. He reaches 10 minutes late to his college when he is having an average speed of 30 km/hr. However, with a speed of 40 km/hr, he reaches his college 5 minutes earlier. Find the distance between his house and college.
Distance = Speed * Time
Average Speed = 2 x y / (x+y) Kmph.
Average Speed = 3 x y z / ( xy + yz+zx) Kmph
TRICK 1: When 2 different speeds are given and total time taken to cover the entire distance is given, then we can find the distance from one side by this formula-
Distance from one end =(Product of two speeds)*(Total time taken)/(Addition of two speeds)
Example :
A girl goes to school with the speed of 6km/hr and returns with the speed of 5 km/hr. If she takes 5.5 hours in all then the distance in km between her house and school is:
- 30 kms
- 15 kms
- 32.5 kms
- 27.5 kms
Solution- Now, the speeds are 6 km/h and 5 km/h and the total time taken is 5.5 hours.
The distance from college to house can be calculated by putting the values in the formula mentioned above.
Required Distance= (6*5) * 5.5/ (6+5) = 15 kms.
Note : distance for both the speeds being same so entire distance is twice the distance from one side.
TRICK 2: When 2 different speeds are given along with 2 different arrival times, then the distance can be found by
Required Distance = (Product of the speeds)*(Difference between the arrival times) / (Difference of the two speeds)
Distance = S1 *S2 *(diff of time ) / (S1~ S2)
Example:
A boy covers a certain distance between his college and house on bike. He reaches 10 minutes late to his college when he is having an average speed of 30 km/hr. However, with a speed of 40 km/hr, he reaches his college 5 minutes earlier. Find the distance between his house and college.
- 20 km
- 40 km
- 30 km
- 25 km
A man on tour travels first 160 km at 64 km/hr and the next 160 km at 80 km/hr. The average speed for the first 320 km of the tour is:
Solution:
Let x= 64 km/hr and y = 80 km/hr
Average speed = (2xy) / (x+y)
= 2*64*80/ (64+80)
=10240/144 = 71.11 km/hr
