[tex] Primul \ robinet \ are \ debitul \ d_1 \ , \ iar \ cel \ de-al \ doilea \ are \ debitul \ d_2=d_1+5\frac{l}{min}.Primul \ robinet \ umple \ piscina \ in \ t_1=90min \ , \ iar \ al \ doilea \ in \ t_2=90min-30min=60min. [/tex]
[tex] Notam \ cu \ V-volumul \ piscinei : [/tex]
[tex] V=d_1t_1 [/tex]
[tex] V=d_2t_2=(d_1+5\frac{l}{min})t_2 [/tex]
[tex] d_1t_1=(d_1+5)t_2 [/tex]
[tex] d_1t_1=t_2d_1+5t_2 [/tex]
[tex] d_1t_1-t_2d_1=5t_2 [/tex]
[tex] d_1(t_1-t_2)=5t_2 [/tex]
[tex] d_1=\frac{5t_2}{t_1-t_2}=10\frac{l}{min} [/tex]
[tex] Volumul \ piscinei \ este:V=d_1t_1=900l [/tex]