A girl travels along a straight road due east for the first half distance with speed `v_(1)` and the second half distance with speed `v_(2)` . What is the average speed of the girl ?

Explanation

Given :
Total distance = s
Let the velocity of the girl for the first half distance be `v_(1)`
Let the velocity of the girl for the second half distance be ` v_(2)`
Formula :
Time taken `= ("Distance")/("Velocity") `
Time taken for the first half distance
`=((s)/(2))/(V_(1)) = (S)/(2v_(1))`
Time taken for the second half distance
`= ((s)/(2))/(v_(2))= (S)/(2v_(1))`
`{:("Total time"),("taken"):}} = (S)/(2v_(1)) +(S)/(2v_(2))`
Average speed ,
`v_(av)= (S)/((s)/(2v_(1))+(s)/(2v_(2)))=(2v_(1)v_(2))/(v_(1)+v_(2))`