Question 425353
Well, not quite!
Think about how much salt there is in the initial solution.
280(0.2) = 56 ml of salt.
You are not adding any salt to make the new solution, just water, so the amount of salt will be unchanged, only its concentration changes. So...
280(0.2) = (x+280)(0.14) x is the amount of water you will add.
56 = 0.14x + 39.2 Subtract 39.2 from both sides.
16.8 = 0.14x Divide both sides by 0.14
x = 120
So you would need to add 120 ml. of water to the 280 ml. of 20% salt solution to get 400 ml. of 14% salt solution.
Check:
280(0.2) = (280+120)(0.14)
56 = 400(0.14)
56 = 56