Question

Морська вода віщує 5% солі за масою. Скільки прісної води треба додати до 30 кг морської, щоб концетрація солі зменшилась на 70%?

Answer 1

30*5/100 + х*0/100=(30+х)*1,5/100
150=45+1,5х
1,5х=105
х=70кг

Answer 2

Calculating Freshwater Addition to Reduce Salt Concentration

To calculate the amount of freshwater needed to reduce the salt concentration in the seawater, we can use the concept of initial and final concentrations.

Given: - Initial salt concentration in seawater: 5% by mass - Amount of seawater: 30 kg - Desired reduction in salt concentration: 70%

First, let's calculate the initial amount of salt in the seawater:

Initial amount of salt in seawater: ``` Initial salt amount = 5% of 30 kg Initial salt amount = 0.05 * 30 kg Initial salt amount = 1.5 kg ```

Now, we need to find the final amount of salt in the mixture after adding freshwater to achieve a 70% reduction in salt concentration.

Final amount of salt in the mixture: ``` Final salt amount = 30% of initial salt amount Final salt amount = 0.30 * 1.5 kg Final salt amount = 0.45 kg ```

To find the amount of freshwater needed, we can use the concept of conservation of mass. The total mass of the mixture (seawater + freshwater) will remain constant.

Let's denote: - Mass of freshwater to be added: x kg

The total mass of the mixture after adding freshwater will be 30 kg (seawater) + x kg (freshwater).

The final concentration of salt in the mixture is 30% of the initial concentration. We can use this information to solve for x.

Calculating the amount of freshwater to be added: ``` Final salt concentration = Final salt amount / (30 kg + x kg) 0.30 = 0.45 kg / (30 kg + x kg)

Solving for x: 0.30 * (30 kg + x kg) = 0.45 kg 9 kg + 0.30x kg = 0.45 kg 0.30x kg = 0.45 kg - 9 kg 0.30x kg = -8.55 kg x kg = -8.55 kg / 0.30 x ≈ -28.5 kg ```

It seems that the calculated value for x is negative, which indicates an error in the calculation. Let's re-evaluate the problem to ensure accuracy.