A car traveled 40% of the way from Town X to Town Y at an average speed of 40 mph. The car traveled at an average speed of v mph for the remaining part of the trip. The average speed for the entire trip was 50 mph. What is v in mph?  Choose the correct choice from the following answers:  A) 50  B) 45  C) 55  D) 60  E) 65

Rationale: "assume total distance = 100 miles time taken for 40 miles = 40 / 40 = 1 hour time taken for the rest of the 60 miles = 60 / v hours . average speed = 50 therefore the total time needed = 2 hours . 2 = 1 + 60 / v hence v = 60 mph answer : d"
Answer: D