......................=5/504
1) 6 1/7 - 3 17/36=6 36/252 - 3 119/252=2 169/252
2) 2 169/252 * 2,5=2 169/252 * 5/2=2 * 5/2+169/252 * 5/2=5+845/504=6 341/504
3) 4 1/3 :0,65=13/3 * 20/13=20/3=6 2/3
4) 6 341/504 - 6 2/3=341/504 - 2/3=341/504 - 336/504=5/504