a) 4/7 : 16/49 = 4/7 * 49/16 = (4 * 49)/(7 * 16) = (4 * 7 * 7)/(7 * 4 * 4) = 7/4 = 1 3/4
в) 12/25 : 8/15 = 12/25 * 15/8 = (12 * 15)/(25 * 8) = (3 * 4 * 3 * 5)/(5 * 5 * 2 * 4) = 9/10