5/6*9/15-5/12*4/15, 7/18*9/14-5/12*4/15, 9/20*2/3+5/14*7/25,

1) 5/6 * 9/15 - 5/12*4/15 =

= (5*9) / (6*15) - (5*4) / (12*15) =

= (1*3) / (2*3) - (1*1) / (3*3) =

= 1/2 - 1/9 = 9/18 - 2/18 = 7/18

2) 7/18*9/14 - 5/12*4/15=

= (7*9) / (18*14) - (5*4) / (12*15) =

= (1*1) / (2*2) - (1*1) / (3*3) =

=1/4-1/9 = 9/36 - 4/36 = 5/36

3) 9/20*2/3 + 5/14*7/25=

= (9*2) / (20*3) + (5*7) / (14*25) =

= (3*1) / (10*1) + (1*1) / (2*5) =

= 3/10 + 1/10 = 4/10 = 2/5