Question

The distance between adelaide and melbourne is 450 miles. For the first 200 miles, Mila drives her car at X miles per hour. For the remaining distance, Mila drives her car at (X+30) mph. The average speed of the whole trip is 30 mph. What is the value of X?

Answer 1

First part of the trip:
Time taken= 200/x

Second part of the trip:
Time taken= 250/(x+30)

Average:
Time taken= 450/30
Time taken= 15 hours

200/x + 250/(x+3)= 15
-15x^2+405x+600=0
x=28.40805152