In a race of 90km Alex finished the first 30km at an average speed of 108km/h and the second 30km at 50 m/s. At what time should he complete the last 30 km to finish the race at an average speed of 144km/h.
a)20m 50s b)22m 40s c) 15m 42s d) 25m

• Time = Distance/Speed or, t=d/s
  
  so,
  t3 = time taken in last 30kms of journey
  = 30/144 hours
  = 750 seconds
  = 25 minutes
  Option (d)
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