(1)6.01-1.9+4.99-2.1,
=(6.01+4.99)-(1.9+2.1),
=11-4,
=7;
(2)0.25×32×12.5,
=(0.25×4)×(8×12.5),
=1×100,
=100;
(3)0.65×64-65×0.54,
=0.65×64-0.65×54,
=0.65×(64-54),
=0.65×10,
=6.5;
(4)90÷(3.6-1.8),
=90÷1.8,
=50;
(5)52+6.5+26×0.37,
=58.5+9.62,
=68.12;
(6)0.36÷[(6.1-4.6)×O.8],
=0.36÷[1.5×O.8],
=0.36÷1.2,
=0.3.