Posted by Katherine on .
How do I work this problem? "Susan is 9 years older than Karen. In 10 years Karen will be 2/3 Susan's age. How old will the two girls be in 10 years?"

Algebra 
Zoe,
I just guessed and checked for this one, but the answer is Karen will be 18, and Susan will be 27.

Algebra 
PsyDAG,
Process: Let S = Susan's current age and K = Karen's
S = K + 9
2/3(S + 10) = K + 10
Substitute K+9 for S in second equation and solve for K. Insert that value into the first equation and solve for S. Check by inserting both values into the second equation. Add 10 to each age.