Adruggist has two mixtures of a certain chemical and water, one containing 10% of the chemical and the other containing 40% of the chemical. how much of each mixture should he use to make 10 ounces that contain 25% of the chemical? how many ounces of chemical are in the final mixture?

Let x be the amount of the solution containing 10% of the chemical. Then, the solution with 40% chemical becomes 10 - x. The equation for balancing the chemical content of the solution is, 
                                    0.10x + 0.40(10 -  x) = 0.25(10)
The value of x is 5. Hence, the druggist should mix 5 ounces of each. There are 2.5 ounces of chemical in the final mixture.

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.