Question 835031
you let x equal the concentration of salt in the final solution.
your formula becomes:


.21(20) + .12(10) = x(30)
this equation becomes:
4.2 + 1.2 = x(30)
this simplifies to:
5.6 = x(30)
divide both sides of this equation by 30 to get:
x = 5.6/30 = .1867 rounded to the fourth decimal digit.
confirm by multiplying 30 * .1867.
you should get something close to 5.6.
you'll get much closer or right on if you don't round.