Andrew Geller

Andrew Geller is a top GMAT tutor based out of New York City. Throughout his career he has successfully taught people from many different backgrounds, countries, and starting scores.

A contractor combined x tons of a gravel mixture that contained 10 percent gravel G, by weight, with y tons of a mixture that contained 2 percent gravel G, by weight, to produce z tons of a mixture that was 5 percent gravel G, by weight. What is the value of x?

A contractor combined x tons of a gravel mixture that contained 10 percent gravel G, by weight, with y tons of a mixture that contained 2 percent gravel G, by weight, to produce z tons of a mixture that was 5 percent gravel G, by weight. What is the value of x? (1) y =

A contractor combined x tons of a gravel mixture that contained 10 percent gravel G, by weight, with y tons of a mixture that contained 2 percent gravel G, by weight, to produce z tons of a mixture that was 5 percent gravel G, by weight. What is the value of x? Read the Full Article »

Tanya prepared 4 different letters to be sent to 4 different addresses. For each letter, she prepared an envelope with its correct address. If the 4 letters are to be put into the 4 envelopes at random, what is the probability that only 1 letter will be put into the envelope with its correct address?

  A. 1/24 B. 1/8 C. 1/4 D. 1/3 E. 3/8 Good old Tanya’s letters! The first time I saw this question it stumped me. Mostly because I took to long to solve it by trying to be overly math-y and complicated. Here’s a quick reminder to: stay practical! There are no awards for elegance

Tanya prepared 4 different letters to be sent to 4 different addresses. For each letter, she prepared an envelope with its correct address. If the 4 letters are to be put into the 4 envelopes at random, what is the probability that only 1 letter will be put into the envelope with its correct address? Read the Full Article »

In the xy-plane, does the line with equation y = 3x + 2 contains the point (r,s)?

(1) (3r+2−s)(4r+9−s) = 0 (2) (4r−6−s)(3r+2−s) = 0 This is a challenging geometry and system of equations/algebra question from the GMAT prep tests 1 and 2. We see this one pretty often in GMAT tutoring sessions so you’re not alone in seeking some assistance. It’s important to remember that with GMAT geometry, often, the geometry

In the xy-plane, does the line with equation y = 3x + 2 contains the point (r,s)? Read the Full Article »

If n is a positive integer and r is the remainder when (n – 1)(n + 1) is divided by 24, what is the value of r?

If n is a positive integer and r is the remainder when (n – 1)(n + 1) is divided by 24, what is the value of r? (1) n is not divisible by 2 (2) n is not divisible by 3 A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient. B.

If n is a positive integer and r is the remainder when (n – 1)(n + 1) is divided by 24, what is the value of r? Read the Full Article »