If each lap is 400 meters long, then 3 laps will have a total distance of 400*3 = <<400*3=1200>>1200 meters
The total time he ran was 70 on the first lap + 85 on the second one and 85 on the third lap, so his total running time was = 70+85+85 = <<70+85+85=240>>240 seconds
His average speed then is measured by the total distance he ran (1200) divided by the total time required (240) or 1200/240 = <<1200/240=5>>5 m/s
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