(1)(5.81-2.09)×3.5,
=3.72×3.5,
=13.02;
(2)2.5×8×0.5+40,
=2.5×4×2×0.5+40,
=(2.5×4)×(2×0.5)+40,
=10×1+40,
=10+40,
=50;
(3)3.865+1.92+3.135+2.08,
=(3.865+3.135)+(1.92+2.08),
=7+4,
=11;
(4)5.8×6.1+3.2×6.1+6.1,
=(5.8+3.2+1)×6.1,
=10×6.1,
=61;
(5)16÷0.25÷0.4,
=16÷(0.25×0.4),
=16÷0.1,
=160;
(6)(750-366)÷48×[25÷(210-209)],
=384÷48×[25÷(210-209)].
=384÷48×[25÷1],
=384÷48×25,
=8×25,
=200.