(20+20/21)÷20
=(20+20/21)×1/20
=20×1/20 +20/21×1/20
=1+1/21
=1又1/21
5分之4×8分之1+5分之1÷8
=4/5×1/8+1/5×1/8
=(4/5+1/5)×1/8
=1×1/8
=1/8
(20+20/21)÷20
=(20+20/21)×1/20
=20×1/20 +20/21×1/20
=1+1/21
=1又1/21
5分之4×8分之1+5分之1÷8
=4/5×1/8+1/5×1/8
=(4/5+1/5)×1/8
=1×1/8
=1/8