Lizzy: Bob's school track is 400 meters. If Bob ran the first lap in 70 seconds, the second and third lap in 85 seconds each, what was his average speed in (m/s) for his entire run?.
Me: Hmmm, let me think. I think this is the detailed solution:
If each lap is 400 meters long, then 3 laps will have a total distance of 400 * 3 = 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 = 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 = 5 m / s. Final answer: 5.