Question

0,78: ( x+0,002)=390; 7,8: (x-0,002)=3900

Answer 1

0,78 : ( X + 0,002 ) = 390 
X + 0,002 = 0,78 : 390 
X + 0,002 = 0,002
X = 0,002 - 0,02 
X = 0 

7,8 : ( X - 0,002 ) = 3900 
X - 0,002 = 7,8 : 3900 
X - 0,002 = 0,002 
X = 0

Answer 2

$1)\frac{0.78}{x+0.002} =390 /*(x+0.002)\\ 0.78=390x+0.78 \\ 390x+0.78=0.78 \\ 390x=0 \\ x=0$

$2) \frac{7.8}{x-0.002} =3900/*(x-0.002) \\7.8=3900x-7.8 \\ 3900x=7.8+7.8 \\ 3900x=15.6 \\ x=0.004$