Express 25cm as a fraction of 3m
1 m = 100 cm
1 cm = 1 / 100 m
25 cm = 25 / 100 m = 0.25 m = 1 / 4 m
25 cm / 3 m = ( 1 / 4 m ) / 3 m = 1 / 4 ∙ 3 = 1 / 12
OR
1 m = 100 cm
3 m = 300 cm
25 cm / 3 m = 25 cm / 300 cm = 25 ∙ 1 / 25 ∙ 12 = 1 / 12