7/8x2/3x9/14
原式=7/8x3/7
=3/8
(5/9-1/3)÷8/15
原式=(5/9-3/9)÷8/15
=2/9x15/8
=5/12
(1+1/4)÷(1-1/4)
原式=5/4÷3/4
=5/4x3/4
=5/3