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Question

Sachin covers a certain distance by car driving at 80 km/h and he returns to the starting point riding on a scooter at 50 km/h. Find his average speed for the whole journey up to 2 decimal places.

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
61.54 km/h

Average Speed Calculation for Car and Scooter Journey

The average speed is defined as the total distance traveled divided by the total time taken.

For a journey where an object travels the same distance at two different speeds, $v_1$ and $v_2$, the average speed ($V_{avg}$) can be calculated using the harmonic mean formula:

$ V_{avg} = \frac{2 v_1 v_2}{v_1 + v_2} $

Step-by-Step Calculation

  1. Identify the speeds for each part of the journey.
    • Speed of car ($v_1$) = 80 km/h
    • Speed of scooter ($v_2$) = 50 km/h
  2. Apply the average speed formula for equal distances: $ V_{avg} = \frac{2 \times 80 \times 50}{80 + 50} $
  3. Calculate the numerator: $ 2 \times 80 \times 50 = 2 \times 4000 = 8000 $
  4. Calculate the denominator: $ 80 + 50 = 130 $
  5. Divide the numerator by the denominator: $ V_{avg} = \frac{8000}{130} = \frac{800}{13} $
  6. Convert the fraction to a decimal and round to two decimal places: $ V_{avg} \approx 61.53846... \text{ km/h} $ Rounded value: $ V_{avg} = 61.54 \text{ km/h} $

Final Answer

The average speed for the whole journey is approximately 61.54 km/h.

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Similar Questions

  1. Wasim travels 455 km at 91 km/hr, the next 390 km at 78 km/hr and the next 476 km at 68 km/hr. What is his average speed (in km/hr) for the whole journey? (Round off your answer to two decimal places)
  2. Heena covers a certain distance by train at 110 km/h and she returned to the starting point covering the same distance, driving a car at 50 km/h. Find her average speed for the whole journey.
  3. A man completes a journey in 11 h. He travels first half of the journey at the speed of 25 km/h and the second half at the speed of 30 km/h. Find the total distance of the journey.
  4. An aeroplane flies along the sides of an equilateral triangle at the speed of 300 km/h, 200 km/h and 240 km/h, respectively. The average speed of the plane while flying around the triangle is:
  5. If a motor car travels the first half of a distance at a speed of 30 km/h and the remaining half distance at a speed of 50 km/h, what will be its average speed?
  6. What is Ram's average speed if he goes from Point X to Point Y at 8 km/hr and returns from Point Y to Point X at 12 km/hr?
  7. A bus covers the first 50 km of its journey in 95 min and covers the remaining 70 km in 85 min. What is the average speed of the bus?
  8. A man rides his bicycle for 10 km at an average speed of 12 km/h and further travels 12 km at an average speed of 10 km/h. What is his approximate average speed for the entire trip?
  9. A person starting from his house covers a distance at 15 km/hr and returns to the starting place at a speed of 10 km/hr. His average speed during the whole journey is:
  10. A man completes 30 km of a journey at 6 km/hr and the remaining 40 km of the journey in 5 hr. His average speed for the whole journey is:

Important Questions from Average Speed

  1. A car runs first 275 km at an average speed of 50 km/h and the next 315 km at an average speed of 70 km/h. What is the average speed ( in km/h) for the entire journey?

  2. Akhil rides first 12 km at a speed of 16 km/h and further 6 km at a speed of 20 km/h. Find his average speed (in km/h).

  3. Shyam drives his car 30 km at a speed of 45 km/h and, for the next 1 h 20 m, he drives it at a speed of 51 km/h. Find his average speed (in km/h) for the entire journey.

  4. X and Y travel a distance of 90 km each such that the speed of Y is greater than that of X. The sum of their speeds is 100 km/h and the total time taken by both is 3 hours 45 minutes. The ratio of the speed of X to that of Y is:

  5. If a man travels at \(\frac{1}{x}\) km/h on a journey and returns at  \(\rm \frac{1}{x^2}\) km/h, then his average speed for the journey is:

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