2- 3/8÷7/17-1/7 =2-3/8×17/7-1/7=2-51/56-1/7=53/565/12÷8+18×7/12 =5/12×8+8×7/12+10×7/12=8+35/6=13又5/63/8÷【（1/2+1/3）×3/30】=3/8÷（5/6×3/30）=3/8÷1/12=3/8×12=9/2