[1÷(1-0.99)]÷(1-0.999)
=〔1÷0.01]÷0.001
=100÷0.001
=100000
1/8×(0.65+7/20)÷1/7
=1/8×(0.65+0.35)÷1/7
=1/8×1÷1/7
=7/8