A person covers a certain distance with certain speed if he increases his speed by 08 km/hr then he reach 10 min early . By how much time he will be late if he reduced his speed by 8 km/hr, if his initial speed is 40 km/hr .

15 min

Initial speed = 40 km/hr 

And speed increases by 8 km/hr ,

Increased speed = ( 40 + 8 ) km/hr= 48 km/hr

Ratio             initial speed     :      increased speed

                         40              :           48 

speed                 5               :            6 

time                   6               :            5

 ( Distance = Speed × Time , so ratio of speed and time is inverse to each other  ) 

According to question , ( 6 - 5 )R = 10 min 

Time taken with initial speed of 40 km/hr = 6 × 10 = 60 min 

Now , when speed is decreased by 8 km/hr 

Decreased speed = ( 40 - 8 ) = 32 km/hr 

Ratio             initial speed     :      decreased speed

                         40              :           32 

speed                 5               :            4 

time                   4               :            5

As ,  4R = 60 min 

1R = 15 min

Difference in time = ( 5 - 4 )R  ⇒   1R = 15 min