What is the greatest possible speed at which a person can walk 13.3 km and 20.9 km so that the time (in hours) required in each case is a whole number?

For time to be a whole number, speed must divide both 13.3 and 20.9 exactly. We need the HCF of 13.3 and 20.9. Multiply by 10: HCF of 133 and 209. 133 = 7 × 19, 209 = 11 × 19. HCF = 19. So HCF of 13.3 and 20.9 = 1.9. Check: 13.3/1.9 = 7 hours, 20.9/1.9 = 11 hours. Both whole. Greatest speed = 1.9 km/h.