Question 1043564
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Salt usually/(sometime? always?) is a crystal solid body or a powder media.


And it is not measured in milliliters. It is measured in grams, for such a situation.


And the concentration, in this case, is (gram/gram) dimensionless measure.


So, if the solution is 45 gram in mass, then there is 


{{{45*(20/100)}}} = {{{45*(1/5)}}} = {{{45/5}}} = 9 gram of salt.