Question

3.058. Морская вода содержит 5% соли по массе. Сколько пресной воды нужно добавить к 30 кг морской воды, чтобы концентрация соли составляла 1,5%?

Answer 1

60 кг воды надо добавить 

Answer 2

Calculation:

To solve this problem, we need to determine the amount of fresh water that needs to be added to 30 kg of seawater to achieve a salt concentration of 1.5%.

Let's break down the problem step by step:

1. Calculate the amount of salt in 30 kg of seawater: - Seawater contains 5% salt by mass. - Therefore, the amount of salt in 30 kg of seawater is 5% of 30 kg. - Amount of salt in 30 kg of seawater = 5/100 * 30 kg = 1.5 kg.

2. Determine the desired concentration of salt after adding fresh water: - The desired concentration of salt is 1.5%. - Therefore, the amount of salt in the final solution should be 1.5% of the total mass of the final solution.

3. Calculate the total mass of the final solution: - The total mass of the final solution is the sum of the mass of seawater and the mass of fresh water added. - Let's assume the mass of fresh water added is 'x' kg. - Therefore, the total mass of the final solution is 30 kg (mass of seawater) + 'x' kg (mass of fresh water added).

4. Set up an equation to solve for 'x': - The amount of salt in the final solution is 1.5% of the total mass of the final solution. - Therefore, the amount of salt in the final solution is 1.5/100 * (30 kg + 'x' kg). - We can set up the equation as follows: 1.5/100 * (30 kg + 'x' kg) = 1.5 kg (amount of salt in 30 kg of seawater).

5. Solve the equation for 'x': - Multiply both sides of the equation by 100 to eliminate the decimal. - Simplify the equation: 1.5 * (30 + 'x') = 150. - Distribute 1.5: 45 + 1.5 * 'x' = 150. - Subtract 45 from both sides: 1.5 * 'x' = 105. - Divide both sides by 1.5: 'x' = 70.

Answer:

To achieve a salt concentration of 1.5% in the final solution, you need to add 70 kg of fresh water to 30 kg of seawater.

Please let me know if there's anything else I can help you with!