If a car had traveled 40 kmh faster than it actually did, the trip would have lasted 30 minutes less. If the car went exactly 120 km, at what speed did it travel? Choose the correct choice from the following choices:
A) 50 kmh B) 60 kmh C) 70 kmh D) 80 kmh E) 90 kmh

Rationale: "time = distance / speed difference in time = 1 / 2 hrs 120 / x - 120 / ( x + 40 ) = 1 / 2 substitute the value of x from the options . - - > x = 80 - - > 120 / 80 - 120 / 120 = 3 / 2 - 1 = 1 / 2 answer : d"
Answer: D