robinet 1………6 ore ……1 bazin
robinet 1….......1 ora…….1/6 din bazin
robinet 2………4 ore ……1 bazin
robinet 2….......1 ora…….1/4 din bazin
r1+r2…….....1 ora……1/6+1/4=5/12 din bazin
r1+r2……….x ore…… 1 bazin
x=1:(5/12)=12/5 (ore)
12/5 ore= 2,4 ore=2ore si 24 minute
sau: 12/5 ore=12•60 minute/5=144 minute= 2ore si 24 minute