Family A and Family B have a nanny as a 3 day a week nanny share. Nanny wants to arrive 5 minutes late (9.05) and leave 5 minutes early (6.55) every day as it fits with her trains. Otherwise she’d be waiting 20 minutes at the beginning and end of the day for her trains (if she arrived on time and left on time). Family A doesn’t mind, but Family B thinks if you start at 9.05 you finish at 7.05 (meaning a 20 minute wait for the next train). Who is right?