1) 5 + 1/4 - 5/6 = 5 1/4 - 5/6 = 5 3/12 - 10/12 = 63/12 - 10/12 = 53/12= 4 5/12
2) 7/88 * (8/21 + 8/7)=7/88 * (8/21 + 24/21)=7/88 * 32/21 = 4/33
3) (1 - 7/8 + 7/10) : 3/8 - 2/5 = (1/8 + 7/10):3/8 - 2/5= (5/40 + 28/40):3/8 - 2/5 = 33/40 : 3/8 - 2/5 = 11/5 - 2/5 = 9/5 = 1 4/5
4) (3 - 1 5/8) * (4 - 1 3/11) : (5 - 1 3/11) = 11/8 * 30/11 : 41/11 = 15/4 : 41/11 = 165/164 = 1 1/165