A car travels 60 km at x km/h, 90 km at y km/h, 120 km at z km/h. If average speed = 60 km/h, x = 30 km/h, y = 45 km/h, find z.
Show answer & explanation
Correct answer: C
Explanation
Given:
Distance₁ = 60 km, Speed x = 30 km/h
Distance₂ = 90 km, Speed y = 45 km/h
Distance₃ = 120 km, Speed z = ?
Average Speed = 60 km/h
According to the formula:
Average Speed = Total Distance / Total Time
Total Distance = 60 + 90 + 120 = 270 km
Total Time = 270 / 60 = 4.5 hours
Time₁ = 60 / 30 = 2 hours
Time₂ = 90 / 45 = 2 hours
Time₃ = 4.5 − (2 + 2) = 0.5 hours
z = Distance₃ / Time₃ = 120 / 0.5 = 240 km/h