Question

Doua robinete curg intr-un bazin. Primul robinet umple singur bazinul in 6 ore, , iar al doilea robinet, curgind singur, umple bazinul in 4 ore. In cite ore cele doua robinete curgind impreuna pot umple bazinul.

Answer 1

Fie t=capacitatea bazinului

Intr-o ora, Primul robinet umple  t/6
Intr-o ora Al doilea robinet umple  t/4.

Fie x=numarul de ore necesare ca cele doua robinete, curgand impreuna, sa umple bazinul.
Avem:
$x( \frac{t}{6} + \frac{t}{4} )=t \\ \\ x( \frac{2t}{12} + \frac{3t}{12})=t\\ \\x* \frac{5t}{12}=t\\ \\ x=t* \frac{12}{5t} = \frac{12}{5}=2,4$
Raspuns: 2 ore si 0,4*60=24min