4 - (4 21/40 - 3,25) : 1 9/20 = 3 целых 7/58
1) 4 21/40 - 3 1/4 = 4 21/40 - 3 10/40 = 1 11/40
2) 1 11/40 : 1 9/20 = 51/40 : 29/20 = 51/40 * 20/29 = (51*1)/(2*29) = 51/58
3) 4 - 51/58 = 3 58/58 - 51/58 = 3 7/58
Пояснения:
0,25 = 25/100 = 1/4 - сократили на 25
1 11/40 = (1*40+11)/40 = 51/40
1 9/20 = (1*20+9)/20 = 29/20