=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