Выполните действиям: а) 13/18 + 7/12; б) 5/7 - 3/5; в) 5/6-3/8-1/12.

а) 13/18 + 7/12=26/36 + 21/36=47/36 = 1 11/36

б) 5/7 - 3/5=25/35 - 21/35=4/35

в) 5/6-3/8-1/12=20/24-9/24-2/24=9/24=3/8

13/18 + 7/12 = (13*2) / (18*2) + (7*3) / (12*3) =

= 26/36 + 21/36 = (26+21) / 36 = 47/36 = 1 целая 11/36

5/7 - 3/5 = (5*5) / (7*5) - (3*7) / (5*7) =

= 25/35 - 21/35 = (25-21) / 35 = 4/35

5/6 - 3/8 - 1/12 = (5*4) / (6*4) - (3*3) / (8*3) - (1*2) / (12*2) =

= 20/24 - 9/24 - 2/24 = (20-9-2) / 24 = 9/24 =

= (9:3) / (24:3) = 3/8