Solution:
Since, the three persons start walking together.
Therefore, The minimum distance covered by each of them in complete steps = LCM of the measures of their steps
= LCM (40, 42, 45)
40 = 2 x 2 x 2 x 5 = 23 x 5
42 = 2 x 3 x 7
45 = 3 x 3 x 5 = 32 x 5
=> LCM (40, 42, 45) = 23 x 32 x 5 x 7
= 2520
=> Each person should walk a minimum distance of 2520 cm in complete steps.