9/17÷7+1/7×8/17
=9/17×1/7+1/7×8/17
=(917+8/17)×1/7
=1×1/7
=1/7
（50-1/2）*10.6-49.5*0.6
=49.5*10.6-49.5*0.6
=49.5*(10.6-0.6)
=49.5*10
=495