(2 1/2 * 0,8 - 5 2/3 : 5,1) : 2/3 - 1/3 = 1
1) 2 1/2 * 0,8 = 2,5 * 0,8 = 2
2) 5 2/3 : 5,1 = 17/3 : 51/10 = 17/3 * 10/51 = (1*10)/(3*3) = 10/9 = 1 1/9
3) 2 - 1 1/9 = 1 9/9 - 1 1/9 = 8/9
4) 8/9 : 2/3 = 8/9 * 3/2 = (4*1)/(3*1) = 4/3 = 1 1/3
5) 1 1/3 - 1/3 = 1