3/5(3/5)×(1/3)=(1/5)(1/5)×(1/3)=(1/15)(1/15)×(1/3)=(1/45)(1/45)×(1/3)=(1/135)(1/135)×(1/3)=(1/405)规律：前一个数乘以三分之一等于后一个数五分之三,五分之一,十五分之一,(四十五分之一),一百三十五分之...