Heuristics to highlight

Use suitable numbers (instead of algebra), Use equations/algebra, Aim for subgoals.

A man is in a hurry to get on a plane. While walking as fast as he can in the airport, he notices that the lace on one of his shoes is untied. The untied shoelace will not slow him down but he must arrive at the embarkation gate with the lace tied. There are travelators (moving horizontal pedestrian carriers) in some sections of the airport along his way. Should he tie his lace on ‘stationary’ ground or on the travelator?