On a morning walk, three persons step off together

We have to find the LCM of 40 cm, 42 cm and 45 cm to get the required minimum distance.

For this, $40=2 \times 2 \times 2 \times 5$,

$42=2 \times 3 \times 7$

and $45=3 \times 3 \times 5$

$\therefore$ $\operatorname{LCM}(40,42,45)=2 \times 3 \times 5 \times 2 \times 2 \times 3 \times 7$

$=30 \times 12 \times 7=210 \times 12$

$=2520$

Minimum distance each should walk 2520 cm. So that, each can cover the same distance in

complete steps.