3/4: 5/6 + 2целых 1/2 *2/5 - 1: 1целая 1/6

3/4 : 5/6 + 2 целых 1/2 * 2/5 - 1 : 1 целая 1/6 = 1 целая 3/70

1) 3/4 : 5/6 = 3/4 * 6/5 = (3*3)/(2*5) = 9/10 
2) 2 цел 1/2 * 2/5 = 5/2 * 2/5 = 10/10 = 1
3) 1 : 1 цел 1/6 = 1 : 7/6 = 1 * 6/7 = 6/7
4) 9/10 + 1 = 1 целая 9/10
5) 1 цел 9/10 - 6/7 = 1 цел 63/70 - 60/70 = 1 цел 3/70

Пояснения:
2 целых 1/2 = (2*2+1)/2 = 5/2
1 целая 1/6 = (1*6+1)/6 = 7/6
9/10 = 63/70 - доп.множ. 7
6/7 = 60/70 - доп.множ. 10