A sport car going at an average speed of 108 km/h takes 15 minutes to complete a lap on a racing track. How much speed (in km/h) should be increased to complete the lap in 9 minutes?
Answer & explanation
Correct answer: option 3
Usual speed = 108 km/h
Time = 15 minutes
Distance = Speed × Time
= 108 × \(\frac{15}{60}\) = 27 km
Speed required to cover 27 km in 9 minutes ,
Speed = \(\frac{27× 60 }{9}\) = 180 km/h
Difference in Speed = 180 - 108 = 72 km/h
So , Speed is increased by 72 km/h .