1) а) 4/7-11/14=8/14-11/14=-3/14
б) -4/9-5/12= -16/36-15/36 = -31/36
в) -14/25*20/21=-2/5*4/3= -8/15
г) 14/9:(-16/15) = -14/9*15/16= -7/3*5/8= -35/24 = -1.11/24
2) -8/25*15/14-11/48*(-8/7)= -4/5*3/7+11/6*1/7 = -12/35+11/42 = -72/210+55/210 = -17/210
3) а) -8/19*(13/15+2/15)= -8/19*15/15 = -8/19*1 = -8/19
б) 24/25*(37/43-37/43+15/16) = 24/25*15/16= 3/5*3/2=9/10 = 0,9
4) 1/28 +1/21 = 3/84+4/84 = 7/84 = 1/12
ответ 12