Suppose you have $12,000 to invest. if part is invested at 10% and the rest at 15%, how much should be invested at each rate to yield 12% on the total amount invested?

X=invested at 10%12000-x=invested at 15% .10x+ (.15)(12000-x)=1440 ;; 12% of the total amount is 12% of $12000. .10x + 1800-.15x=1440
-0.05x=-360x=7200 12000-x=4800 $7200 at 10%=$720$4800 at 15%=$720 That is $12000 earning $1440, and that is 12%