Question

Karina travels 70 miles at an average speed of 50 mph.

She then travels a further 60 miles.
The average speed for the entire journey is 44 mph.
Assuming Karina didn't stop, what was her average speed for the final 60 miles to 2 dp?​

Answer 1

Her speed on the second part of the trip was approximately 38.59 mph.

Explanation:

Karina's route is composed of two stages, the first one has a length of 70 miles, while the other has a length of 60 miles. The sum of time she took to complete each stage must be equal to the total time of the trip. Applying the formula for average speed we have:

`time_(total) = (130)/(44) = 2.955 \text{ h}`

`time_(1) = (70)/(50) = 1.4 \text{ h}`

`time_(2) = (60)/(x)`

`time_(total) = time_1 + time_2\\2.955 = 1.4 + (60)/(x)\\(60)/(x) = 2.955 - 1.4\\(60)/(x) = 1.555\\1.555*x = 60\\x = (60)/(1.555) = 38.59 \text{ mph}`

Her speed on the second part of the trip was approximately 38.59 mph.