How would I prepare 500 ml of a 20% salt solution? What is the Molarity of this solution?

http://www.saltinstitute.org/About-salt/Physical-properties
tells us that near room temp, 20 C,... a 20% NaCl solution has a density of 1.14779 grams / ml

that's 1147.8 grams per litre
20% of 1147.8 grams = 229.56 grams of NaCl

using molar mass
229.56 grams of NaCl @ 58.44 g/mol = 3.928 moles of NaCl per litre

What is the Molarity of this solution
your molarity of the 20% NaCl solution is 3.93 Molar
(you might be expected to round off, your data only has 1 sig fig showing)
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How would I prepare 500 ml of a 20% salt solution?
1/2 of 229.56 grams of NaCl = 114.8 grams NaCl

I would dissolve 115 grams of NaCl into some water, then dilute with water up to a total volume of 500 ml