Question 791448
You have to use trial and error. 


Here are 3 ways I found to do it


1/2*6+5*7*8/4+3*9 = 100


4/1*8+2*3*5/6+7*9 = 100

 
6/2*1+5*7*8/4+3*9 = 100


I'm sure there are tons more ways to do it.