Ответ:
Пошаговое объяснение:
1) 0,4/2,8+2/7= 4/10 : 2 8/10 + 2/7 = 4/10 : 28/10 +2/7 = 4/10*10/28 + 2/7= 4/28+2/7= 4+8 / 28 = 12/28 = 3/ 7
2) 2,1/0,3 +7,2/0,9 = 2 1/10 : 3/10 + 7 2/10 : 9/10 = 21/10 :3/10 + 72/10: 90/10 = 21/10* 10/3 + 72/10*10/90 = 21/3+72/90 = 21 + 2160 / 3 = 2181/3 = 727
3) 5,6/8 * 3,5/ 0,7 = 5 6/10 : 8 * 3 5/10 : 7/10 = 56/10 : 8/1 * 35/10 :7/10 = 56/10*1/8 * 35/10 * 10/7 = 7/10*35/10 *10/7 = 35/10 = 3,5
4) 1/2 - 3/4 : 2 = 1/2-0,75/2= 05-0,375=-0,875
5) 0,2/2 *3,5 = 2/10 :2/1 *3,5 = 2/10*1/2 * 3,5 = 0,1 *3,5 = 0,35
6) (7,8/0,6 -4 ) *1/3 = ( 7 8/10 : 6/10 -4 ) *1/3 = (78/10 : 6/10 - 4 ) *1/3 = (78/10*10/6 - 4) *1/3= (78/6-4)*1/3 = (13-4) *1/3 = 9 * 1/3 = 9/3 = 3