Multiple choice

Libby is traveling to another city. She covers the first two hours of her journey at 40 miles per hour. She is getting late, so she drives her car fast, and covers the last 3 hours of the journey at twice the speed she was travelling before. What is her average speed of travel for the entire journey?

  1. 56.67 mph

  2. 64 mph

  3. 66.23 mph

  4. 68 mph

  5. 70 mph
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Distance 1 = 2 hours * 40 mph = 80 miles. Speed 2 = 2 * 40 = 80 mph. Distance 2 = 3 hours * 80 mph = 240 miles. Total distance = 320 miles. Total time = 5 hours. Average speed = 320 / 5 = 64 mph.

AI explanation

The initial speed of 40 miles per hour for 2 hours covers a distance of 80 miles, and the doubled speed of 80 miles per hour for 3 hours covers 240 miles. Using the average speed formula, total distance divided by total time, we get 320 miles divided by 5 hours. This results in an average speed of 64 mph for the entire journey.

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