(20.01+20.02+20.03+20.04+20.05+20.06+20.07+20.08+20.09)÷9

问题描述:

(20.01+20.02+20.03+20.04+20.05+20.06+20.07+20.08+20.09)÷9
简便~

20.04+20.06=40.10=2*20.05,20.03+20.07=40.10=2*20.05...
括号内总共有9个20.05相加,除以9得20.05