Question
A car travels from A to B, a distance of 180 km. It
covers the first 60 km at 40 km/h, the next 60 km at 60 km/h and the last 60 km at 90 km/h. Find the approximate average speed for the whole journey.Solution
Time for first 60 km = 60 / 40 = 1.5 hours Time for next 60 km = 60 / 60 = 1 hour Time for last 60 km = 60 / 90 = 2/3 hour Total time = 1.5 + 1 + 2/3 = 2.5 + 0.666… = 3 1/6 = 19/6 hours Total distance = 180 km Average speed = Total distance / Total time = 180 ÷ (19/6) = 180 × (6/19) = 1080/19 km/h ≈ 56.84 km/h.
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