1÷17×89-9÷二又八分之一
= 1÷17×89 - 9÷(2+1/8)
= 1/17×89 - 9÷17/8
= 89/17 - 9×8/17
= 89/17 - 72/17
= (89 - 72)/17
= 17/17
= 1