（7/6-6/7）*42%=（49/42-36/42）*42%=13/42*0.42=13*0.01=0.13
（7/6-1÷7/6）×42%＝（7/6-6/7）×0.42＝7/6×0.42-6/7×0.42＝0.49-0.36＝0.13
