2道简便计算,12分之5除21分之10乘0.15（用简便计算）,第二道：3分之2除（5分之4－15分之8）＋6分之1,完

(5/12) / (10/21) X 0.15
= (10/24) / (10/21) X 15/100
= (1/24) / (1/21) X 3/20
= ( 21 / 24 ) X ( 3 / 20 )
= ( 7 X 3 ) / ( 8 X 20 )
= 21 / 160
(2/3) / ( 4/5 - 8/15 ) + 1/6
= (10/15) / ( 12/15 - 8/15 ) + 1/6
= 10 / ( 12 - 8 ) + 1/6
= 10 / 4 + 1/6
= 15/6 + 1/6
= 16 /6
= 8 /3
= 2+ 2/3