A manufacturer has 600 litres of a 12%12 \% solution of acid. How many litres of a 30%30 \% acid solution must be added to it so that acid content in the resulting mixture will be more than 15%15 \% but less than 18%18 \% ?

Answer: The manufacturer must add more than 120120 litres but less than 300300 litres of the 30%30\% acid solution.

Step-by-step solution

Step 1: Define variables and initial acid content

Let xx be the volume (in litres) of the 30%30\% acid solution to be added. The initial solution has a volume of 600 litres and contains 12%12\% acid. We need to find the range of xx such that the final mixture's acid concentration is between 15%15\% and 18%18\%.

Step 2: Calculate total acid and total volume in the mixture

First, calculate the amount of acid in the initial 600 litres of 12%12\% solution. Then, express the amount of acid in the xx litres of 30%30\% solution. The total acid in the mixture will be the sum of these two amounts, and the total volume will be the sum of the initial volume and xx.

Step 3: Set up inequalities for the acid concentration

The problem states that the acid content in the resulting mixture must be more than 15%15\% but less than 18%18\%. This can be written as an inequality where the ratio of total acid to total volume is between 0.150.15 and 0.180.18.

Step 4: Solve the first inequality

We solve the first part of the inequality: the acid concentration must be greater than 15%15\%. Multiply both sides by (600+x)(600 + x), distribute, and then isolate xx to find its lower bound.

Step 5: Solve the second inequality

Next, we solve the second part of the inequality: the acid concentration must be less than 18%18\%. Similar to the previous step, multiply by (600+x)(600 + x), distribute, and isolate xx to find its upper bound.

Step 6: Combine the inequalities

By combining the results from both inequalities, we find the range of xx for which the acid content in the resulting mixture will be more than 15%15\% but less than 18%18\%.

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