solution % and salt water

Question

a 10% solution of salt in water means 10grams of salt for every 100 grams of salt water solution. you are given 100grams of a 10% solution of salt in water and wish to change it to a 30% solution of salt in water. how many grams of salt would you need to add to the solution?

Answer 1

10% salt means 10 grams salt for every 100 grams of salt water solution

to change it to 30% how many grams of salt should be added?

.1(100) + 1.00s = .3(100+s)

10+ s = 30+.3s

.7s = 20

s = 20/.7 = 200/7 = about 28.57 grams of salt

38.57/128.57 = .29999... = about .3 = 30% salt solution