Evaluate the two proposed answers. Which are supported? I. stream speed in km/h when downstream speed is 18 and upstream speed is 10 — the numerical answer in the stated units: 15. II. catch-up time in hours for a 60 km/h vehicle starting 30 km behind a 45 km/h vehicle — the numerical answer in the stated units: 2.
Correct answer: C
I is incorrect: stream speed in km/h when downstream speed is 18 and upstream speed is 10 → 4. Stream speed is (18−10)/2. II is correct: catch-up time in hours for a 60 km/h vehicle starting 30 km behind a 45 km/h vehicle → 2. Relative speed is 15 km/h; time=30/15.