Obshee kratnoje u 3 i 13 = 39.....
1/3 = 13/39
2/3 = 26/39
proverim drobi mejdy 13/39 i 26/39 :
13/39 - nelzya zapisat so znamenatelem 13, tak kak 13 ne delitsya na tri....
14/39 - nelzya
15/39 = 5/13..... RAZ.
16/39 - nelzya
17......- nelzya
18/39 = 6/13 ..... DVA
19/39 .... nelzya
20/39..... nelzya
21/39 = 7/13......tri...
po analogii......22,23,25,26 - nelzya (napominajy, 26/39 - eto konets nashego diapazona)
ostaetsya CHETYRE - 24/39 = 8/13...
Itogo otvet: 5/13 6/13 7/13 8/13