посчитайте у нас сейчас самостоятельная ​

1 . 1/3 + ( 3/7 + 1/6 ) = ( 1/3 + 1/6 ) + 1/7 = 3/6 + 1/7 = 1/2 + 1/7 = 9/14 .

2 . 1/12 + x = 3/4 + 1/6 ;

1/12 + x = 11/12 ;

x = 11/12 - 1/12 ;

x = 10/12 = 5/6 .

3 . 6 9/20 - ( 2 2/5 + 2 5/8 ) = 6 9/20 - 4 41/40 = 6 9/20 - 5 1/40 = 1 17/40 .