Question 1165786
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Let x be the number of these (7liters+5liters) portions in 636 liters of the mixture.  Then


    7x + 5x = 636

    12x     = 636

      x     = 636/12 = 53  portions.


<U>ANSWER</U>.  53*7 = 371 liter of the natural oil.
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Solved.