Question

Peter usually travels from town P to town Q in eight hours. One day, he increased his average speed by 5km per hour so that he arrived 20 minutes earlier. Find his usual average speed, in km per hour.

Answer 1

Usual time taken by Peter                           = 8 hours
20 minutes earlier than usual time                = 8 - 20/60 
                                                                 = 8 - 1/3
                                                                 = 7 2/3
His speed                                                  = 5 kmph
In 7 2/3 hours he will cover                          = 7 2/3 × 5
                                                                = 23/3 × 5
                                                                =115/3
                                                                ≈ 38.3
Therefore, distance covered by Peter           = 38.3
His speed = Distance travelled / time taken = 38.3/8  
                                                               = 4.79 kmph

Answer 2

4.79 kmph is the answer.