=5. 1×0.2+4.9×0.2

=0.2×(5. 1+4.9)

=0.2× 10

=2

②(8/9+ 1/6)×72%

=8/9×0.72+ 1/6×0.72

=0.64+0. 12

=0.76

③3/4÷(75%+5/8)

=3/4÷(3/4+5/8)

=3/4÷ 1 1/8

=3/4×8/ 1 1

=6/ 1 1

④ 125%×7.6- 1.25×3. 1+ 10/8×5.5

= 1.25×(7.6-3. 1+5.5)

= 1.25× 10

= 12.5