The solution contains 160 g of water and 40 g of salt. How much water do you need to add to reduce the salt content by 4?

First, we find out how much salt will become if we reduce the mass of water by 4 grams, if it is known that it was 40 grams:

40 – 4 = 36.

Now let’s determine how much a solution of salt and water weighs together, if the mass of each is known:

160 + 40 = 200 grams.

Next, we find how many grams of water will be in the solution if we reduce the mass of salt by 4 grams:

200 g solution – 40 g salt,

x g of solution – 36 g of salt.

x = 200 * 36/40

x = 180

Now you can find out how much water you need to add:

180 – 160 = 20

Answer: you need to add 20 grams of water.