5/9× 21/5+18/5÷9/7简便计算
问题描述：
5/9× 21/5+18/5÷9/7简便计算
答
5/9× 21/5+18/5÷9/7
=7/3+18/5*7/9
=7/3+14/5
=35/15+42/15
=77/15
5/9× 21/5+18/5÷9/7
=1/9*1/5*(5*21+18*7)
=1/45*(105+126)
=1/45*231
=77/15