A car travels 60 km at 30 km/h, 90 km at 45 km/h, 150 km at z km/h. If average speed = 60 km/h, find z.
Show answer & explanation
Correct answer: B
Explanation
Given:
Distance₁ = 60 km, Speed₁ = 30 km/h
Distance₂ = 90 km, Speed₂ = 45 km/h
Distance₃ = 150 km, Speed₃ = z km/h
Average Speed = 60 km/h
According to the formula:
Average Speed = Total Distance / Total Time
Total Distance = 60 + 90 + 150 = 300 km
Total Time = 300 / 60 = 5 hours
Time₁ = 60 / 30 = 2 hours
Time₂ = 90 / 45 = 2 hours
Time₃ = 5 − (2 + 2) = 1 hour
z = Distance₃ / Time₃ = 150 / 1 = 150 km/h