Но делаем в скобках (7/15-1/6)+2/5; (3/8-1/9)+25/36; (8/9-5/6)+2/3; (7/8-13/20)+9/10; 7/18-1/12)+5/6; 3/4-8/15)+17/20

( 7/15 - 1/6 ) + 2/5 = 9/30 + 2/5 = 21/30 = 7/10
( 3/8 - 1/9 ) + 25/36 = 19/72 + 25/36 = 69/72 = 23/24
( 8/9 - 5/6 ) + 2/3 = 1/18 + 2/3 = 13/18
( 7/8 - 13/20 ) + 9/10 = 9/40 + 9/10 = 45/40 = 1 5/40 = 1 1/8
( 7/18 - 1/12 ) + 5/6 = 11/36 + 5/6 = 41/36 = 1 5/36
( 3/4 - 8/15 ) + 17/20 = 13/60 + 17/20 = 64/60 = 1 4/60 = 1 1/15