№399
- 3/4 + (- 5 1/4) = - (3/4 + 5 1/4) = - 6
-11 3/4 + (-5 3/4) = - (11 3/4 + 5 3/4) = - (16 + 6/4) =
=- (16 + 3/2) = - (16 + 1 1/2) = - 17 1/2
-7/8 + (-1/4) = -(7/8 + 1/4) = - ( 7/8 + 2/8) = - 9/8 = - 1 1/8
-9/11 +(-4 3/11) = - (9/11 + 4 3/11) = - 5 1/11
-9/14 +(-8 1/6) = - (9/14 + 8 1/6) = - (27/42 + 8 7/42)=
= - 8 34/42 = - 8 17/21