Time & Distance

Time & Distance

We need to remember the below formulas before proceeding on Time & Distance questions

Speed = (Distance/Time) è Time = (Distance/Speed)  è Distance = Speed*Time

1Km per hour (Kmph) = 5/18 m/Sec è 1m/sec = 18/5 Km per hour

Tip1: If a person travels a distance from point ‘P’ to point ‘Q’ at X Kmph and back to point ‘P’ at ‘Y’ Kmph. Then average speed = 2XY/(X+Y)

Tip2: If a person travels a distance from point ‘P’ to point ‘Q’ at a speed of ‘X’ Kmph and returns at a speed of ‘Y’ Kmph and takes ‘T’ hours in all. Then the distance between P and Q = T*(XY/X+Y)

Tip3: Ratio of the speeds of P and Q is X:Y, then the ration of the times to cover the same distance is 1/X : 1/Y or Y:X

Tip4: If a scooterist covers a distance in ‘T’ hrs. The first half in ‘X’ Kmph and the second half in ‘Y’ kmph. The total distance covered by the Scooterist  is (2*T*X*Y)/(X+Y)

Ex: If a car completes a journey in 8hrs. It covers half the distance at 20Kmph and the rest in 40Kmph. The total distance of the journey is:

Sol: Use Tip4

ð  (2*T*X*Y)/(X+Y)  = (2*8*20*40)/(20+40) = 213.33 Km

Ex: Ratio of the speeds of person A and B is 3:4.if the time taken by B to cover a distance is 36mins, then time taken by A to cover that much distance is?

Sol: Tip3

ð  Ration of the speeds of A and B = 3:4

ð  Ratio of the time = 1/3 : 1/4= 4:3

ð  If B takes 3 min then A takes 4mins  è if B takes 36mins then A takes 36*(4/3) è 48mins

Ex: If a person walks at 5kmph for 6hrs and at 4kmph for 12hrs. The average speed of the man is:

Sol:

ð  Total distance covered = (5*6 + 4*12) = 78km

ð  Total time taken = 6+12 = 18hrs

ð  Average Speed = D/T => 78/18 = 13/3 Kmph

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