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What is the average speed of a journey that takes 4 hours at 27.5 km/h and then 7 hours at 48.5 km/h?

a) 36.5 km/h
b) 35 km/h
c) 37.5 km/h
d) 40 km/h

User Ramtin
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1 Answer

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Final answer:

The average speed of the journey is calculated by summing the distances traveled at each speed and dividing by the total time. With 4 hours at 27.5 km/h and 7 hours at 48.5 km/h, the average speed is approximately 40.9 km/h. The closest answer choice is (d) 40 km/h.

Step-by-step explanation:

Calculating Average Speed

To find the average speed of a journey that has different speeds for different parts, we must first determine the total distance traveled and then divide it by the total time. The journey consists of 4 hours at 27.5 km/h and then 7 hours at 48.5 km/h. We calculate the distances for each segment as follows:

  • Distance1 = Speed1 × Time1 = 27.5 km/h × 4 h = 110 km
  • Distance2 = Speed2 × Time2 = 48.5 km/h × 7 h = 339.5 km
  • Total Distance = Distance1 + Distance2 = 110 km + 339.5 km = 449.5 km
  • Total Time = Time1 + Time2 = 4 h + 7 h = 11 h

We then use the formula for average speed, which is:

Vavg = Total Distance / Total Time

Plugging in the values:

Vavg = 449.5 km / 11 h = 40.8636 km/h

The correct answer rounded to the nearest tenth is 40.9 km/h. However, since none of the answer choices exactly match this value, we choose the closest answer, which is (d) 40 km/h.

User Pontomedon
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