50:х - 50:(100-х) = 5/12.

  [latex]\frac{50}{x} - \frac{50}{100-x} = \frac{5}{12}\\\\ x \ne 0, x \ne 100\\\\ \frac{50}{x} - \frac{50}{100-x} = \frac{5}{12} | * (100-x)x12\\\\ 12(5000-50x) -12*50x = 5(100-x)x\\\\ 12(1000-20x) = 100x-x^2\\\\ x^2 -340x +12000 = 0\\\\ x_1*x_2 = 12000 =300*40\\\\ x_1+x_2 = 340\\\\ x_1 = 300\\\\ x_2 = 40[/latex]