(3/7-3/7×7/8)÷1/2
=3/7(1-7/8)×2
=3/56×2
=3/28
2/7×(1÷3/4-3/4÷1)
=2/7×(4/3-3/4)
=2/7×(7/12)
=2/12
=1/6