(1)1÷(6-1.25×0.8),
=1÷(6-1),
=1÷5,
=0.2;
(2)[2/15]÷([19/21]+[3/7])×[1/2],
=[2/15]÷[4/3]×[1/2],
=[2/15]×[3/4]×[1/2],
=[1/20];
(3)([7/8]-[7/16])×([5/9]+[1/3]),
=[7/16]×[8/9],
=[7/18].
(1)1÷(6-1.25×0.8),
=1÷(6-1),
=1÷5,
=0.2;
(2)[2/15]÷([19/21]+[3/7])×[1/2],
=[2/15]÷[4/3]×[1/2],
=[2/15]×[3/4]×[1/2],
=[1/20];
(3)([7/8]-[7/16])×([5/9]+[1/3]),
=[7/16]×[8/9],
=[7/18].