3/20 • (7/12 -1/2 ) + 79/80
_______________________ =
13/24 : (7/12 + 1/2 ) - 1/4

7/12-1/2=7/12-6/12=1/123/20×1/12=1/801/80+79/80=80/80=17/12+1/2=7/12+6/12=13/1213/24÷13/12=13/24×12/13=1/21/2-1/4=2/4-1/4=1/41÷1/4=1×4/1=4ответ 4