№1
а) 12/13 * (-2/5) =- 24/65;
б) - 15/16 * 3/4 = - 45/64;
в) 12/13 * 1/5 = 12/65.
№2
а) 9 * (-11/27) = -99/27 = -11/3 = - 3 2/3;
б) - 12/5 * 15/4 = - 180/20 = - 9;
в) 27/28 * 14/81 = 378/2268 = 1/6.
№3
3 * 16 * 17 * 18 * 19 * 20 3 * 20
---------------------------------- = ---------- = 4.
15 * 16 * 17 * 18 * 19 15
№4*
а) - 26/27 * 1/13 = - 26/351 = - 2/27;
б) -2 * 5/4= -2,5;
в) 35 * 1/14 = 35/14 = 2,5.