20 +30 : 2 = 50 :2 =25 minute
si akum aplicam pe regula de 3 simpla d. proportionala :
4 minute .................................. 200 litri
25minute .................... x
25 x 200 : 4 =5000 : 4 =1250 ( cp bazin)
problema asta am facut-o in clasa a6 -a