FAIRGROUND CIRCLES
Janet started on the Big Wheel at the same moment that Barry started on the Twirler and Sheila started on the Rotator. The Big Wheel went round once every ten seconds, the Twirler once every seven seconds and the Rotator once every eight seconds.
If all three children started at the bottom of their respective rides, how long would it have been before they were in line with each other again at the bottom of each ride?