Speed = total distance/ total time Calculation: Distance covered in 5 hours (7 : 30 A.M. to 12 : 30 P.M.) =30%×500=150km ⇒ Now initial speed of the cab=150∕5=30km∕ hours ⇒ Remaining distance =500−150=350km ⇒ Remaining time ( 12 : 30 P.M. to 07 : 30 P.M.) = 7 hour ⇒ Now speed of the cab =350∕7=50km∕ hours ∴ Difference between initial and last speed =50−30=20km∕ hour