The OG13 has flaws, as did its predecessors. Why five stars, then? Because, hands down, this latest incarnation of the OG is still the one book to get, if you can only get one book to prepare for the GMAT with. There's simply no better all-in-one source of retired GMAT problems.

Could the explanations be better? Sure.

Could the GMAT folks have replaced more than just 1 in 6 problems from the OG12? Absolutely.

Why did some repeated problems illogically jump the line backwards or forwards, given that both OG12 and OG13 are supposed to be in order of difficulty? Who knows.

All that said, the OG is still THE primary religious text of the GMAT. Everything else--including all that we write in print or in byte--is commentary.

The 158 new problems in OG13 all exude that sweet, ineffable air of GMAT-ness. Even if you're taking the GMAT before the changeover (on June 5), in your shoes I'd buy this book for those new problems alone. In the grand scheme, I'd consider that a good investment.

If you're taking the GMAT on June 5 or after, you also need to prepare for the new Integrated Reasoning section. This book gives you access to 50 IR practice problems on a separate site online. Another reason to purchase.

Now, on to the analysis...

Analysis of the 13th Edition Official Guide

(This analysis was originally published with additional content at [...])

The 13th Edition of the Official Guide for GMAT Review has finally been released publicly. Here at Manhattan GMAT, we've done an initial analysis of the OG13 book.

1. Not Radically Different

OG13 contains 907 practice problems for the "main" part of the GMAT (Quant & Verbal). Of those 907 problems, only 17% are new. Since you know your fraction equivalents, we don't have to tell you that 17% is about 1 out of 6.

Out of 907 problems, 749 are repeats (yes, that's 5 out of 6). If you already have the 12th Edition, a good way to look at the 13th Edition is as a source of 158 great new practice problems. We've listed them by number at the end of this post.

Much of the book is unchanged from the 12th Edition:

- For repeated problems, the explanations are identical, except for a few extremely minor edits (e.g., fixing an error in numbers chosen to test Statement 1 in DS #135).

- Various sections, such as the Diagnostic Exam (all 100 problems), Math Review, Test-Taking Strategies and Directions, are unchanged.

- Each of the 5 major types (PS, DS, RC, CR, and SC) has the same number of problems as before: 254 PS, 198 DS, 156 RC, 141 CR, and 158 SC.

- Excluding the Diagnostic Exam, practice questions are organized by difficulty, according to the GMAC--just as they are in the 12th edition--but with an asterisk we'll explain below.

We've done all the new problems, and they're just what you'd expect--good, clever GMAT problems. Each one has its own unique flavor, but they're all from the same big box of cookies. Given that only 1 in 6 are new, we don't ascribe too much meaning to the unavoidable micro-shifts in topical balance.

Do not over-interpret changes from OG12 to OG13! Some variation is to be expected. Nothing suggests a shift in how you should prepare for the exam.

2. Transition If And When You're Comfortable

If you've been getting ready with the 12th Edition, treat the 13th Edition as a source of additional practice. But you do not need to switch, especially if your exam is before June 5, when the new GMAT arrives.

If you're taking an "old" GMAT, consider mining the 13th Edition for a few new problems. But your time may be better spent reviewing practice problems you've already encountered. Or you might just do online practice with GMATPrep, GMATFocus, or practice exams such as ours.

3. Integrated Reasoning is Integrated

If you are taking the "new" GMAT (on or after June 5), the OG13 has some relevant goodies for you: a short introduction to IR, plus access to 50 brand-new practice problems online. Even though the IR section won't count for much in the admissions process, you don't want to face it completely cold. Running through these 50 problems will help warm you up.

In fact, you might catch fire and start freaking out about IR. If that happens, go dunk your head in water. IR is not that important. You just want to give it a decent shot. Save your strength for the main event of the GMAT.

4. Order Oddities

Both OG12 and OG13 claim to be laid out in order of difficulty (except for the 100 Diagnostics). Since all the problems are retired from the real exam, that order should never change--so you'd expect repeated problems to maintain their relative positions in the hierarchy.

Weirdly, though, 25 repeated problems have jumped out of position. Here are the rebels:

Problem Solving:

13th Ed.|12th Ed.|Change

20 203 -183

25 200 -175

31 64 -33

55 196 -141

65 28 37

67 201 -134

95 106 -11

109 69 40

126 228 -102

132 93 39

181 202 -21

Data Sufficiency:

13th Ed.|12th Ed.|Change

4 47 -43

38 134 -96

53 165 -112

58 171 -113

67 30 37

78 137 -59

81 58 23

119 173 -54

120 147 -27

125 107 18

128 157 -29

135 128 7

143 161 -18

166 132 34

While we've understood and agreed with the OG difficulty ordering in broad strokes, we've always wondered about some of the specific rankings. Is Marcia's Bucket (DS #174) truly the hardest DS problem on the planet, three editions running--11th, 12th, and 13th? That one has always bewildered us.

The reshuffle is generally in the right direction, if we were doing the ranking of those 25 problems. For instance, we think that PS #69 in the 12th is harder than PS #196 in the 12th, not conceptually but in actual execution. Old #69 is tricky! Now the new numbering (#109 and #55, respectively, in OG13) reflects that opinion.

However, the mystery is why this reshuffling is happening at all. If the problems were in relative order of difficulty in one edition, any repeats should stay in that order till the end of time--since the problems are most definitely retired!

This weird reordering happened before on a smaller scale, when the supplemental Review OGs transitioned from 1st to 2nd Editions. One problem in each slipped out of position. That level of change could be chalked up to clerical error or to random genetic mutation caused by a stray cosmic ray or what have you.

However, with 25 problems on the quant side (and none on the verbal side) acting illogically, we can only guess at something larger. It should be straightforward for the GMAT to measure difficulty--it's a basic parameter for each question, a single number developed during the problem's experimental stage and then frozen. Perhaps, for a whole batch of questions, these parameters were recorded in a systematically erroneous way, and now GMAC is fixing the problem. Maybe the way GMAC measures difficulty has some quirks to it, and under an update to the algorithm these problems would somehow get a different ranking.

Regardless, we don't think there's anything nefarious to all this--there's no reason that GMAC would deliberately mess with our heads. After all, the 10th Edition of the OG, for those of us who go back that far, was comfortably chaotic. It had no order whatsoever. The 11th Edition was the first one that the GMAT folks put in order of difficulty--and we all welcomed that change. It made studying so much more productive to know how hard a problem was to the GMAT, if only in relative terms.

As we find out more on this matter, we'll let you all know.

5. Stay Tuned

More generally, as we dig further into OG13, we'll keep you posted on any juicy discoveries. Again, we don't want to squint too hard at the tea leaves. We'll start seeing things that aren't really there: "Is there one more or one less Probability problem, and what signal is the GMAT sending...?" That road leads to madness. This OG is pretty much the same as the last one, just with some new good problems in it.

6. New Problems

And now, what you've been waiting for... here are the new problem lists, all by number in the OG13. We're moving a couple of topics around ourselves, so these breakouts reflect the upcoming topical alignments.

Problem Solving: 12, 13, 14, 15, 37, 49, 56, 57, 60, 61, 69, 71, 75, 77, 78, 79, 80, 81, 91, 92, 108, 110, 112, 113, 114, 117, 118, 119, 127, 128, 129, 137, 158, 163, 166, 170, 177, 178, 182, 183, 196, 198, 199, 218, 229

PS Fractions, Decimals, & Percents: 15, 56, 57, 71, 80, 108, 113, 114, 163, 170, 177, 182, 198, 218

- Digits & Decimals: 163, 170, 218

- Fractions: 15, 80, 108

- Percents: 57, 71, 114, 177, 182, 198

- Ratios: 56, 113

PS Algebra: 14, 37, 117, 129, 196, 199

- Linear Equations: 14

- Exponents & Roots: 196

- Quadratic Equations: 37, 117, 199

- Formulas: 129

PS Word Problems: 12, 49, 60, 79, 81, 91, 112, 119, 137, 158, 178, 183

- Algebraic Translations: 60, 137

- Rates & Work: 49, 79, 81

- Statistics: 12, 91, 112, 119, 183

- Consecutive Integers: 158

- Overlapping Sets: 178

PS Geometry: 13, 61, 69, 75, 78, 92, 166

- Polygons: 13, 78, 166

- Triangles & Diagonals: 75, 92

- Circles & Cylinders: 69

- Coordinate Plane: 61

PS Number Properties: 77, 110, 118, 127, 128, 229

- Divisibility: 77, 110, 118, 127

- Positives & Negatives: 229

- Combinatorics: 128

Data Sufficiency: 11, 15, 18, 20, 22, 23, 24, 25, 29, 32, 33, 34, 37, 39, 41, 42, 52, 57, 65, 70, 74, 75, 79, 80, 83, 85, 92, 96, 97, 99, 102, 109, 123, 131, 133, 141

DS Fractions, Decimals, & Percents: 23, 25, 29, 75, 80, 92, 131, 133

- Digits & Decimals: 75, 80, 133

- Fractions: 29, 92, 131

- Percents: 25

- Ratios: 23

DS Algebra: 15, 24, 33, 41, 52, 85, 96, 99

- Exponents & Roots: 15, 41

- Quadratic Equations: 99

- Formulas: 24, 96

- Inequalities: 33, 52, 85

DS Word Problems: 18, 20, 22, 34, 37, 57, 65, 70, 109, 123, 141

- Algebraic Translations: 57, 65, 141

- Rates & Work: 22

- Statistics: 20, 37, 70, 109, 123

- Consecutive Integers: 18

- Overlapping Sets: 34

DS Geometry: 11, 42, 74, 79, 102

- Polygons: 42

- Triangles & Diagonals: 79

- Circles & Cylinders: 102

- Coordinate Plane: 11, 74

DS Number Properties: 32, 39, 83, 97

- Divisibility & Primes: 83

- Positives & Negatives: 97

- Odds & Evens: 32

- Probability: 39

Reading Comprehension: 1, 2, 3, 4; 11, 12, 13; 14, 15, 16, 17; 37, 38, 39, 40, 41; 52, 53, 54, 55; 84, 85, 86; 111, 112, 113, 114 (passages separated by semicolons)

7 new passages

- Length: 2 long, 5 short (3 of the shorts are just 1 big paragraph, though!)

- Themes: 2 biological science, 2 business, 2 social science, and 1 physical science

Question types:

7 General questions (4 Main Idea, 3 Structure) - roughly 1 per new passage

20 Specific questions (8 Detail, 12 Inference) - roughly 3 per new passage

Since you'd never do all the questions of 1 type at once (you always do RC by passage), there's little point in breaking them out by number.

Critical Reasoning: 1, 3, 6, 8, 9, 11, 12, 17, 19, 22, 29, 33, 39, 49, 59, 65, 69, 74, 81, 86, 94, 100, 106, 114, 124

- Assumption: 106

- Evaluate the Argument: 114, 124

- Flaw: 8, 100

- Strengthen: 1, 11, 19, 29

- Explain the Discrepancy: 3, 6, 9, 17, 22, 49, 86, 94

- Complete the Argument: 12, 33, 39, 59, 65, 69, 74, 81

Sentence Correction: 1, 2, 4, 7, 9, 15, 19, 26, 35, 38, 40, 48, 56, 65, 68, 71, 74, 79, 87, 97, 107, 111, 114, 132, 138

- Subject-Verb Agreement: 7

- Parallelism: 4, 15, 38, 56, 74, 79, 87, 138

- Pronouns: 111, 114

- Modifiers: 1, 19, 35, 48, 65, 68, 132

- Verbs: 40, 71

- Comparisons: 9, 107

- Connecting Punctuation: 2, 26, 97