脱式计算，能简算的要简算．0.42÷[（3.2-0.5）÷9]7.7×9.910.1÷1.25÷0.819.9×99+19.990.23×7+7.3×0.76.9÷[（1.07-0.82）÷2.5]．

Question

脱式计算，能简算的要简算．

0.42÷[（3.2-0.5）÷9]	7.7×9.9	10.1÷1.25÷0.8
19.9×99+19.99	0.23×7+7.3×0.7	6.9÷[（1.07-0.82）÷2.5]．

Answer 1

①0.42÷[（3.2-0.5）÷9]
=0.42÷[2.7÷9]
=0.42÷0.3
=1.4

②7.7×9.9
=7.7×（10-0.1）
=7.7×10-7.7×0.1
=77-0.77
=76.23

③10.1÷1.25÷0.8
=10.1÷（1.25×0.8 ）
=10.1÷1
=10.1

④19.9×99+19.99
=19.9×（100-1）+19.99
=19.9×100-19.9×1+19.99
=1990-19.9+19.99
=1990+19.99-19.9
=1990+0.09
=1990.09

⑤0.23×7+7.3×0.7
=2.3×0.7+7.3×0.7
=（2.3+7.3）×0.7
=9.6×0.7
=6.72

⑥6.9÷[（1.07-0.82）÷2.5]
=6.9÷[0.25÷2.5]
=6.9÷0.1
=69