Express 25cm as a fraction of 3m
25/300 = 1/12
1 m = 100 cm
3 m = 3 • 100 cm = 300 cm
25 cm / 3 m = 25 cm / 300 cm =
25 • 1 / 25 • 12 = 1 / 12
OR
Since 1 m = 100 cm
1 cm = 1 / 100 m
25 cm = 25 / 100 m = 1 / 4 m
25 cm / 3 m =
( 1 / 4 m ) / 3 m = 1 / 4 • 3 = 1 / 12