28.71-7.29+2.29-2.71怎样简算

问题描述:

28.71-7.29+2.29-2.71怎样简算

(28.71-2.71)-(7.29-2.29)=26-5=21

(28.71-2.71)-(7.29-2.29)

(28.71+2.29)-(7.29+2.71)=31-10=21

28.71+2.29-(7.29+2.71)=21