Question 809240
(amount of pure acid)/(amount of solution or mixture resulting)=(concentration of acid in solution or mixture)


Let x = amount of the 27 % acid to use.


{{{(16*18+x*27)/(x+16)=21}}}, or according to the way the choices are presented,
{{{(16*(0.18)+x(0.27))/(x+16)=0.21}}}