Question
A car travels half of a journey at 40 km/h and the
remaining half at 60 km/h. What is the average speed for the whole journey?Solution
Let total distance = 2D km. Then each half = D km. Time for first half = D/40 hours Time for second half = D/60 hours Total time = D/40 + D/60 = (3D + 2D) / 120 = 5D / 120 = D / 24 hours Average speed = Total distance / Total time = 2D ÷ (D/24) = 2D × (24/D) = 48 km/h
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