简算5/6×8+2/5÷4
=5/6×8+2/5×1/4
=20/3+1/10
=20/3+1/10
=203/30

简算15/16+（7/16-1/4）÷1/2
=15/16+（7/16-1/4）×2
=15/16+7/8-1/2
=15/16+14/16-8/16
=21/16