Question 380926
Generating 20:


(5+2)*4-8 = 7*4-8 = 28-8 = 20   


or


(5-2)*4+8 = 3*4+8 = 12+8 = 20 


or


(8-5+2)*4 = 5*4 = 20




Generating 17: 

5+2*8-4 = 5+16-4 = 21-4 = 17



Generating 39: 

It is NOT possible to generate 39 using the given numbers and rules above. I've tried all possible combinations and cannot get 39 (you could get 39 if you allowed two + symbols since 8*4+5+2 = 39)



Generating 13

(8-4)*2+5 = 4*2+5 = 8+5 = 13