SOLUTION: HOW MANY GRAMS OF PURE SALT MUST BE ADDED TO 40 GRAMS OF A 20% SALT SOLUTION TO MAKE A SOLUTION THAT IS 36% SALT?

Question 1844: HOW MANY GRAMS OF PURE SALT MUST BE ADDED TO 40 GRAMS OF A 20% SALT SOLUTION TO MAKE A SOLUTION THAT IS 36% SALT?
Answer by longjonsilver(2297) (Show Source): You can put this solution on YOUR website!
For a 20% salt solution, one fifth (ie 20%) is salt. As we have 40g of the solution, then 8g (ie a fifth) must be salt.
we would work out the % by saying (8/40)*100 = 20%
However, we now will add some more salt. Call this unknown amount, x grams. We therefore increase the amount of salt by 8 and the total amount by 8 too. And the new salinity is 36%. So, we have
Re-arranging this gives

Rearranging this again gives

hence x=10g of salt required.
We can see this in the formula...it is now (18/50)*100 which is 36%
cheers
Jon.
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