(3分之7－5分之3)÷5分之7
=（7/3-3/5）×5/7
=7/3×5/7-3/5×5/7
=5/3-3/7
=26/21
8分之5÷3分之5+5分之3×8分之3
=5/8×3/5+3/5×3/8
=3/8+3/5×3/8
=3/8×（1+3/5）
=3/8×8/5
=3/5