## Articles by Rich Zwelling

#### Is That Number Prime?

by Rich Zwelling on November 15, 2011

Rich presents the easiest way to figure out if a number is prime or not.

#### Be Careful When Interpreting “Must Be True” Questions

by Rich Zwelling on October 29, 2011

#### The Speedy Road to Insufficiency

by Rich Zwelling on October 13, 2011

Should you prove that statements are sufficient or should you prove them insufficient?

#### Intuition and Common Sense on Geometry DS Questions

by Rich Zwelling on September 27, 2011

Who cares about the value of x? Well, on DS, we don't!

#### The AWA Isn’t That Important… So Can I Blow It Off?

by Rich Zwelling on September 22, 2011

Should you sacrifice the AWA for a well-rested mind later on? Rich provides his opinion on this stategy.

#### Tips for Comparing Fractions on the GMAT

by Rich Zwelling on September 13, 2011

Fractions, always a headache! Use Rich's tips to navigate through all the signs and powers.

#### Filling in Your Chart: A Data Sufficiency Primer

by Rich Zwelling on August 29, 2011

Rich breaks down an overlapping sets question, complete with tables to visualize the solution!

#### To Venn or Not to Venn? Depends on the Question

by Rich Zwelling on August 15, 2011

Should you go for Venn diagrams or tables? Both require you to showcase your drawing skills, but most of the time one is quicker than the other.

#### Two Shortcut Formulas for Set Problems

by Rich Zwelling on August 8, 2011

If you're one of those people who goes crazy over overlapping sets problems, this post is for you.

#### More Fun with Weighted Averages

by Rich Zwelling on August 4, 2011

Weighted averages are really useful for Data Sufficiency, but they're not too bad for Problem Solving either.

#### What the Heck is a Weighted Average?

by Rich Zwelling on July 25, 2011

You can bet that weighted average questions will show up in Data Sufficiency!

#### Quick Mental Math: Averages

by Rich Zwelling on July 4, 2011

If the GMAT is more about reasoning than speed calculations, then why am I writing a post on quick mental math?

#### How to Approach Rate Problems on GMAT Quant, Part II

by Rich Zwelling on June 27, 2011

A handy Knewton guide to solving work rate problems.