Ben runs around the track at a pace of 1 lap every 80 seconds. Sally runs on the track in the opposite direction. The two meet every 30 seconds. How long does it take Sally to run each lap around the track?

48 seconds, Consider what happens between one time that Ben and Sally meet and the next. During this period Ben runs 30 (seconds) / 80 (seconds/lap) = 3/8 of a lap. So Sally runs 5/8 lap in the same time. Her speed is therefore 5/8 (laps) / 30 (seconds) which amounts to 1 (lap) / 48 (seconds).