Question

Морская вода содержит 5% соли. Сколько килограммов пресной воды нужно добавить к 40 кг морской воды, чтобы содержание соли в смеси составляло 2%.

Answer 1

Найдем содержание соли в граммах
40:100*5=2 гр
а теперь решаем обратную задачу, но для концентрации 2%
2:2*100=100 л
находим сколько надо добавить пресной воды
100-40=60 л

Answer 2

Calculation of Freshwater Needed to Add to Seawater

To determine how much freshwater needs to be added to 40 kg of seawater to achieve a salt content of 2%, we can use the following calculation:

1. Calculate the amount of salt in the initial mixture of seawater: - The seawater contains 5% salt, so the amount of salt in 40 kg of seawater is 5% of 40 kg. - Amount of salt in 40 kg of seawater = 5% of 40 kg = 0.05 * 40 kg = 2 kg.

2. Calculate the total mass of the final mixture (seawater + freshwater): - Since we want the salt content in the final mixture to be 2%, the total mass of the final mixture will be the sum of the initial mass of seawater (40 kg) and the mass of freshwater to be added. - Let's assume the mass of freshwater to be added is 'x' kg. - Total mass of the final mixture = 40 kg + x kg.

3. Calculate the amount of salt in the final mixture: - The salt content in the final mixture is desired to be 2%. - So, the amount of salt in the final mixture is 2% of the total mass of the final mixture. - Amount of salt in the final mixture = 2% of (40 kg + x kg).

4. Set up an equation to solve for 'x': - The amount of salt in the final mixture should be equal to the amount of salt in the initial mixture. - Therefore, we can set up the equation: Amount of salt in the final mixture = Amount of salt in the initial mixture. - Mathematically, this can be represented as: 2% of (40 kg + x kg) = 2 kg.

5. Solve the equation for 'x': - Simplifying the equation, we get: 0.02 * (40 kg + x kg) = 2 kg. - Solving for 'x', we have: 0.02 * 40 kg + 0.02 * x kg = 2 kg. - 0.8 kg + 0.02 * x kg = 2 kg. - Subtracting 0.8 kg from both sides, we get: 0.02 * x kg = 1.2 kg. - Dividing both sides by 0.02, we find: x kg = 60 kg.

Answer:

To achieve a salt content of 2% in the mixture, you would need to add 60 kg of freshwater to 40 kg of seawater.