SOLUTION: Suppose Mr. Taylor's speed during journey from Pittsburgh to Chicago was 'x' mph. So his speed during journey from Chicago to Pittsburgh was 'x+15' mph. Time taken in up-journey

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: Suppose Mr. Taylor's speed during journey from Pittsburgh to Chicago was 'x' mph. So his speed during journey from Chicago to Pittsburgh was 'x+15' mph. Time taken in up-journey       Log On


   

Question 40887: Suppose Mr. Taylor's speed during journey from Pittsburgh to Chicago was 'x' mph. So his speed during journey from Chicago to Pittsburgh was 'x+15' mph.
Time taken in up-journey = 600%2Fx hrs.
Time taken in down-journey = 600%2F%28x%2B15%29 hrs.
As down-journey takes 2 hrs. more so 600%2Fx+=+600%2F%28x%2B15%29+%2B+2
or 600%2Fx+-+600%2F%28x%2B15%29+=+2
or 9000%2F%28x%2A%28x%2B15%29%29+=+2
or %28x%2A%28x%2B15%29%29+=+9000%2F2+=+4500
or x%5E2+%2B+15x+-+4500+=+0
Factorising
%28x+%2B+75%29%28x+-+60%29+=+0
But here speed cannot be negative (as then the car goes in opposite direction and the problem is not valid) so x not equal to -75.
Hence x = 60.
Ans.: Thus the average speed of Mr. Taylor's car from Pittsburgh to Chicago was 60 mph.
Answer by psbhowmick(878) About Me  (Show Source):