А)- 2 5/7 + 3 = - 19/7 + 3 =(-19*1 + 3 * 7)/7 = -19/7 + 21/7 = 2/7
б) -2/9+(-5/6)=- 2/9 - 5/6 =(-2 * 2-5 * 3)/18 = -4/18 -15/18 = - 19/18 = - 1 1/18
в)2 9/11+(-3 7/22)=2 9/11 - 3 7/22 = 31/11 - 73/22 =(31 * 2 - 73 * 1)/22 = 62/22 - 73/22 = - 11/22 = - 1/2