а) 7/8 + 3/9= 7/8 + 1/3 = (7*3+1*8)/24 = (21+8)/24 = 29/24 = 1 5/24
б) 5 11/12 - 3 7/18 = (5*12+11)/12 - (3*18+7)/18 = 71/12 - 61/18 = (71*3-61*2)/36 = (213-122)/36 = 91/36 = 2 19/36
в) 4 2/5 * 1 1/2 = (4*5+2)/5 * (1*2+1)/2 = 22/5 * 3/2 = (22*3)/(5*2) = 66/10 = 6 6/10 = 6 3/5
г) 1 5/9 : 2 8/27 = (1*9+5)/9 : (2*27+8)/27 = 14/9 : 62/27 = 14/9 * 27/62 = (14*27)/(9*62) = (14*3)/(1*62) = 42/62 = 21/31
Ответ: а) 1 5/24; б) 2 19/36; в) 6 3/5; г) 21/31.