Question 1135355
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Here is a very short and quick alternative to the traditional algebraic solution method shown by the other tutor.<br>
(1) The target percentage of 13% is 3/10 of the way from 10% to 20% -- the percentages of the two ingredients.
(2) Therefore 3/10 of the mixture should be the higher percentage ingredient.<br>
ANSWER:  3/10 of 120 = 36 gallons of 20% fertilizer; 7/10 of 120 = 84 gallons of 10% fertilizer.