数学简便运算
(1)9/10-(1/4+7/20)÷3/4
(2)3/5÷[7/8-(2/5+3/8)]
(3)10/21÷[2/3×(2/7+4/7)]
(4)7/10×5/16÷21/32+1/2
(5)5.64-3.22+2.36-0.78
(6)1/6÷4/9-2/5×3/4