Multiple choice

Out of a total distance of $200$ km covered, first half is covered at the speed of $60$ km/hr and the remaining half is covered at $75$ km/hr . Find the average speed for the whole journey.

  1. $ 21\dfrac{2}{3}$ km/hr
  2. $ 66\dfrac{2}{3}$ km/hr
  3. $ 43\dfrac{2}{3}$km/hr
  4. $ 39\dfrac{2}{3}$ km/hr
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Average speed is total distance divided by total time. Total distance is 200 km. Time for first 100 km is 100/60 = 5/3 hours. Time for second 100 km is 100/75 = 4/3 hours. Total time is 5/3 + 4/3 = 3 hours. Average speed = 200/3 = 66 2/3 km/hr.

AI explanation

Using the formula for average speed when equal distances are traveled at different speeds, the calculation is 2 multiplied by the product of the two speeds divided by their sum. Substituting the given speeds of 60 km/hr and 75 km/hr into the formula gives 2 multiplied by 60 multiplied by 75 divided by the sum of 60 and 75. The numerator calculates to 9000, and dividing this by the denominator of 135 gives 66.66. Therefore, the average speed for the whole journey is 66 2/3 km/hr.

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