解:3/5÷[〔1/5+1/3〕]÷2/9=3/5÷[〔3/15+5/15〕]÷2/9=3/5÷8/15÷2/9=3/5×15/8×9/2=9/8×9/2=81/16
3/5÷[(1/5+1/3)÷2/9]=3/5÷(8/15x9/2)=3/5÷12/5=3/5x5/12=1/4
=3/5÷(8/15×9/2)=3/5×5/12=1/4