1、(4/5-1/4)÷(4/5+1/4) =11/20÷21/20 =11/212、(1/4-1/8)÷(1/4+1/8) =1/8÷3/8 =1/33、[(74*60%)-6.8]÷8 =(44.4-6.8)÷8 =37.6÷8 =4.7