Shawn Berry’s Criticism of The Official Guide for GMAT Review (2015 Quant Review, Problem Solving #2)

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2015 OG Quant Review PS #2. If x/4 is 2 more than x/8, then x =   .

Note: Original equation is not counted as a line in the solution.


Math Lesson: (1) Given 1st line x/4 = x/8 + 2, find in your head the least common denominator of 4 & 8, lcd(4,8)=8.  Amend the first fraction x/4 by multiplying both the numerator (top) and denominator (bottom) by 2.  The 1st line now reads 2x/8 = x/8 + 2.  Collect like terms in 2nd line x/8 = 2.  Cross-multiply in 3rd line: x = 16.  D/C.

To Add/Subtract Fractions: Write 1st line a/2 + a/3 = 10 and in your head find lcd(2,3)=6.  Amend the first fraction by multiplying top & bottom by 3 and the second fraction by multiplying top & bottom by 2.  Your 1st line now reads 3a/6 + 2a/6 = 10.  Collect like terms in 2nd line 5a/6 = 10.  Cross-multiply in 3rd line; find a =12.  D/C.
Write 1st line k/3 – k/5 = 40 and in your head find lcd(3,5)=15.  Amend the first fraction by multiplying top & bottom by 5 and the second fraction by multiplying top & bottom by 3.  Your amended 1st line should now read
5k/15 – 3k/15 = 40.  Collect like terms in 2nd line, 2k/15 = 40.  Cross-multiply in 3rd line; find k = 300.  Double-check.

Character count: The OG writes 3 lines and 25 characters; Shawn Berry writes 2 lines and 9 characters.  The OG solution uses 278% as many characters as necessary.  Each line matters because you can waste 60 seconds to get a second 6-page workbook.  Each character matters because you must answer 37 Quant questions in 75 minutes.

There’s Joy in Repetition: Collect like terms and then Cross-multiply is the same solution that I taught in PS #1.  In contrast, the Official Guide’s solutions to PS #1 and PS #2 vary.  Students learn best when they are taught simple, repetitive solutions.  Students get confused and fail to learn when they are taught varying solutions.

Shawn Berry (550 level). Two less than a/3 is two more than a/2 for what value of a?

A. 24
B. 12
C. 0
D. –12
E. –24

Shawn Berry (600 level).
One-half subtracted from c/3 is one-half added to c/12 for what value of c?

A. 2
B. 3
C. 4
D. 5
E. 6

Shawn Berry (600 level).
  For what value of k does k divided by the quantity k divided k/2 equal to 2?

A. 1/4
B. 1/2
C. 1
D. 2
E. 4

Shawn Berry (650 level).
 For what value of n does one-eight less than one-seventh of n equal one-fifth less than one-sixth of n?

A. 2.70
B. 2.85
C. 3.00
D. 3.15
E. 3.30

Shawn Berry (750 level).
 Five less the quantity b/3 less b/6 is two less than b for what value of b?

A. 3
B. 4
C. 5
D. 6
E. 7

Legal Note
: “The Graduate Management Admissions Council (GMAC) firmly believes that the Official Guide for GMAT Review is all that you need to perform your best on the GMAT … and that no additional techniques or strategies are needed to do well.”  I, Shawn Berry, know better.  I have twice earned a perfect 800 on the GMAT-CAT.  I document that the Official Guide writes inconsistent, inefficient, and downright confusing solutions that take longer than the allotted 2 minutes/question.  Herein I make fair use of GMAC copyrighted material – mostly its confusing solutions – for the transformative educational purpose of teaching students the clear, consistent, and efficient Mathematics, Grammar, and Logic needed to answer GMAT questions in less than 2 minutes.

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