GMAT On Demand: How to Solve for the Value of an Expression (Without Solving for its Variables!)

by Knewton, Mar 10, 2011

As Jess and Rich explain in this video, Data Sufficiency problems often give you more variables than you have equations. This happens for two main reasons:

• You're just given more variables than equations (you know, because it's fun)
• You're given as many variables as equations, but not all the equations are independent

In these cases, you won't be able to solve for the value of every variable in the system. But -- don't be fooled! This doesn't necessarily mean that E is the right answer. Sometimes, you may be able to solve for the value of an expression involving multiple variables -- without actually knowing the value of those variables. Confused yet? Check out the video for a sample problem and a super helpful explanation!

For more DS tips, check out the rest of the installments of this quantitative strategy lesson:

• Don't Solve Data Sufficiency Problems
• Testing Cases in Data Sufficiency
• How to Simplify Data Sufficiency Problems
• Three Classic DS Problems Involving Systems of Equations
• The Basics of Independent and Dependent Equations

And for even more on-demand video help, check out these sessions on Critical Reasoning, Intro to Quant, and Sentence Correction.