document.write( "Question 560466: A man is twice as old as his son. His son is twice as old as his sister. The total age is 84. What is the father's age? \n" ); document.write( "

Algebra.Com's Answer #363893 by josmiceli(19441) $\"\"$ $\"About$

You can put this solution on YOUR website!
Let $\"s\"$ = Son's age
\n" ); document.write( "Let $\"t\"$ = Sister's age
\n" ); document.write( "Let $\"f\"$ = Father's age
\n" ); document.write( "given:
\n" ); document.write( "(1) $\"+f+=+2s+\"$
\n" ); document.write( "(2) $\"+s+=+2t+\"$
\n" ); document.write( "(3) $\"+f+%2B+s+%2B+t+=+84+\"$
\n" ); document.write( "---------------
\n" ); document.write( "This is 3 equations and 3 unknowns, so it's solvable
\n" ); document.write( "(2) $\"+t+=+s%2F2+\"$
\n" ); document.write( "Substitute (1) and (2) into (3)
\n" ); document.write( "(3) $\"+2s+%2B+s+%2B+s%2F2+=+84+\"$
\n" ); document.write( " $\"+4s+%2B+2s+%2B+s+=+168+\"$
\n" ); document.write( " $\"+7s+=+168+\"$
\n" ); document.write( " $\"+s+=+24+\"$
\n" ); document.write( "and
\n" ); document.write( " $\"+f+=+2s+\"$
\n" ); document.write( " $\"+f+=+2%2A24+\"$
\n" ); document.write( " $\"+f+=+48+\"$
\n" ); document.write( "and
\n" ); document.write( " $\"+t+=+s%2F2+\"$
\n" ); document.write( " $\"+t+=+24%2F2+\"$
\n" ); document.write( " $\"+t+=+12+\"$
\n" ); document.write( "The Father is 48, the Son is 24, and the Sister is 12
\n" ); document.write( "check:
\n" ); document.write( "(3) $\"+f+%2B+s+%2B+t+=+84+\"$
\n" ); document.write( "(3) $\"+48+%2B+24+%2B+12+=+84+\"$
\n" ); document.write( "(3) $\"+84+=+84+\"$
\n" ); document.write( "OK \n" ); document.write( "

\n" );