Uzisusa kanjani izinombolo ezimbili?
Ukususa kuwumsebenzi okhomba inani eliphelele lezinto ezikuqoqo lezinto ngemva kokuba inani elithile lezinto lisusiwe esilinganisweni sokuqala.  Unganciphisa izinombolo ezimbili ngokuqala ngokubala kokuqala, okumelela inombolo okumele isuswe kuyo, kanye nokubala kwesibili okumelela inombolo okumele isuswe. Khona-ke susa eyodwa ekubaleni kokuqala ngokuphinda le nqubo ngenani lezinto ezinenani lokukhishwa.  Ukususa akuhlangene, okusho ukuthi indlela okwenziwa ngayo ukukhipha ibalulekile. Ngokwesibonelo, eziyisikhombisa - ezinhlanu (7 - 3) zilingana nezine (= 4) kodwa ezine - eziyisikhombisa (4 - 7) zilingana nezintathu (= -3).