见图
(4/9×7/8-1/3)×9/4=4/9x7/8x9/4-1/3x9/4=7/8-3/4=7/8-6/8=1/8
(4/9×7/8-1/3)×9/4=4/9×7/8×9/4-1/3×9/4=7/8-3/4=7/8-6/8=1/8