Multiple choice

Concentrations of three solutions A, B and C are 20%, 30% and 40% respectively They are mixed in the ratio 3 : 5 : x resulting in a solution of 30% concentration Find x

  1. 5

  2. 2

  3. 3

  4. 4
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Weighted average: (3*20 + 5*30 + x*40) / (3+5+x) = 30. (60 + 150 + 40x) / (8+x) = 30. 210 + 40x = 240 + 30x. 10x = 30. x = 3.

AI explanation

Using the method of alligation on the concentrations of A and B, the ratio of their quantities to achieve a 30 percent mixture is 1 to 1. Since solution A and B are mixed in the amounts of 3 and 5 respectively, they contribute equally to the 30 percent target, meaning solution C must not alter the overall concentration. Therefore, solution C must also have a 30 percent concentration, making x equal to 3.

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