Bonjour,

a. 78/36 : 13/72

= 78/36 x 72/13

= 5616/468

= (468 x 12) / (468 x 1)

= 12

b. 54/74 : 36/37

= 54/74 x 37/36

= 1998/2664

= (666 x 3) / (666 x 4)

= 3/4

c. 125/81 : 75/108

= 125/81 x 108/75

= 13500/6075

= (675 x 20) / (675 x 9)

= 20/9.