(1)28×[4/7]×[3/4],
=28×([4/7]×[3/4]),
=28×[3/7],
=12;
(2)([3/4]-[2/5])×40,
=[3/4]×40-[2/5]×40,
=30-16,
=14;
(3)[12×([1/2]-[1/3])]÷[3/5],
=[12×[1/2]-12×[1/3]]÷[3/5],
=[6-4]÷[3/5],
=2÷[3/5],
=[10/3];
(4)[7/15]×[4/5]+[7/15]÷5,
=[7/15]×[4/5]+[7/15]×[1/5],
=[7/15]×([4/5]+[1/5]),
=[7/15]×1,
=[7/15].