Question:A boy cycles 10 km at 15 km/h and a further 20 km at 20 km/h. Find his average speed over the whole journey.
Answer The time taken to go d k at v km/h. = `d/v` hours. The time taken to cycle 10 km at 15 km/h. = `10/15` = `2/3` hour. The time taken to cycle 20 km at 20 km/h. = `20/20` = 1 hour. The total time taken to cycle 30 km = `1 2/3` hours. The average speed = distance gone/time taken = `30/(1 2/3) = 90/5 = 18 km/h`
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A boy cycles 10 km at 15 km/h and a further 20 km at 20 km/h. Find his average speed over the whole journey.