найдите значение выражения (1/3+ 1/4) x (2/7-1/5)

(1/3+1/4)*(2/7-1/5) = (4/12+3/12)*(10/35-7/35) = (7/12)*(3/35) = 7/12 * 3/35 = (7*3)/(12*35) = (3*7)/(3*4*7*5) = 1/(4*5) = 1/20