Q: A automobile drives for 30 minutes at a speed of 40 kmph, 45 minutes at a speed of 60 kmph, and 2 hours at a speed of 70 kmph. The car's average speed is  

Answer: B

The first car travels for 30 minutes at a speed of 40 kmph. The distance traveled in this time can be calculated using the formula distance = speed x time, which gives us distance = 40 kmph x (30 minutes / 60 minutes) = 20 km.

The car then travels for 45 minutes at a speed of 60 kmph. The distance traveled in this time can be calculated using the formula distance = speed x time, which gives us distance = 60 kmph x (45 minutes / 60 minutes) = 45 km.

The car then travels for 2 hours at a speed of 70 kmph. The distance traveled in this time can be calculated using the formula distance = speed x time, which gives us distance = 70 kmph x 2 hours = 140 km.

The total distance traveled by the car is the sum of the distances traveled in each of the three time periods, which is 20 km + 45 km + 140 km = 205 km.

The total time taken by the car is the sum of the times taken in each of the three periods, which is 30 minutes + 45 minutes + 2 hours = 3.25 hours.

The average speed of the car can be calculated using the formula average speed = total distance / total time, which gives us average speed = 205 km / 3.25 hours = 63.07 km/h.

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