Bunuel
A specialty fertilizer blend contains 40 percent nitrogen and 60 percent potassium by weight. A different blend contains 20 percent nitrogen and 80 percent phosphorus. When these two blends are combined to create a final mixture, the result contains 35 percent nitrogen. If the final mixture weighs 24 kilograms, how many kilograms of phosphorus does it contain?
A. 3.2
B. 3.6
C. 4
D. 4.8
E. 10.8
This is a very classic mixing problem.
What we are doing now - if we want to get as far as possible without formula - we go by logic.
That means, that we need to find any 100%-Combinations, that give us the result of 35%, using 40 and 20.
50/50 would be 30. If we just imagine four blocks like: | 25 % | 25 % | 25 % | 25 % |, we are now in the middle at 50%. Every other tilt to another side would mean an increase/decrease of 5. As we are looking for 35, we tilt to the 40, and get 75% / 25% as a distribution.
Our interest is only at the phosphorus part, and therefore the 25% part.
We now just need to calculate: 25% * 24 * 80% = 4.8.
Therefore, the result must be D)