What is proportional calculation? Proportional calculation is a method of calculating the ratio of two numbers. When we have two numbers A and B, we can find A divided by B. For example, if A is 100 and B is 200, the ratio of A to B is 100÷200 = 0.5. How do you simplify a ratio? A : B = C : D B ☓ C = A ☓ D example x : 9 = 4 : 3 x = 4 ☓ 9 ÷ 3 = 12 12 : 9 = 4 : 3 Various Display aspect ratio 1 : 1 Square 1.33 : 1 (4:3) 35 mm original silent film, TV（NTSC）, IMAX 1.43 : 1 IMAX 70 mm wide film 1.50 : 1 VistaVision, Chromebook, Pixel Notebook PC, Game Boy Advance, the Surface Pro 3 laplet, Surface Studio 1.6667 : 1 A common European widescreen standard, Super 16 mm frame, Nintendo 3DS 1.77 : 1 (16:9)1 HDTV 1.85 : 1 A common US widescreen cinema standard 2.00 : 1 Univisium