Question 1054016
Thinking about a three-part mixture is more difficult than to think about a two part mixture.


s, how much of 100% sand;
235 kilograms, how much of100% cement;
m, how much of the "concrete" mixture at 6.00% cement and 8.00% sand.


These equations are using decimal numbers and not any quantities as percents:


Account for the desired percent cement.
{{{(235+0.06*m)/(235+m+s)=0.14}}}


Account for the desired percent sand.
{{{(s+0.08m)/(235+m+s)=0.16}}}



The arithmetic should be easier than to do the analysis shown, so you could take care of that arithmetic.