用简便方法计算:9I2t2u.R.U6J4J0l5K
(1989+1997+1993+1995+1997+1999+2001)/(1990+1992+1994+1996+1998+2000+2002)=1K(H6O'L4V'A9i9I2t2u.R.U6J4J0l5K