### The GMAT Official Guide 2019 Edition, Part 1

Ah, fall. The days are still pretty long, the snow is a distant memory (for a couple more months at least), and I get to work through the new problems in the GMAT Official Guide 2019 edition!

That’s right, the Official Guide for GMAT® Review 2019, aka the OG, has landed. Let’s dive right in!

If you have already bought the 2018 edition, you’re okay; you can continue to work through that GMAT Official Guide. About 15% of the questions in OG2019 are new. If, later, you feel you want more, you can decide at that point whether you want to get the 2019 OG or whether you want to get some other official-source questions, such as the online Official Practice Questions or GMAT Focus.

Chapter 3 is a Diagnostic test consisting of the same 100 questions that were in the previous editions. The Diagnostic questions are, on the whole, good questions, so I can understand why the makers of the GMAT (GMAC) are not swapping out these questions.

Chapter 4, the math review, has the same math content (it does have a slightly expanded introduction—3 paragraphs vs. 1).

In this installment, we’ll concentrate on chapter 5 (Problem Solving, PS). There are some trends in the mix of new questions that I find really interesting.

Note: I can’t reproduce the text of questions for copyright reasons, but I’ll cite the problem number of any question I discuss so that you can look it up if you do decide to buy the 2019 edition.

#### What’s New in Problem Solving for the GMAT Official Guide 2019 Edition?

There are 35 new Problem Solving problems in the GMAT Official Guide 2019 edition (and 35 old problems were dropped).

As has been the trend for multiple years now, the lowest-numbered new problems (such as #2 and #4) really do just require you to have some basic computation skills. But I noticed even more of a trend throughout toward not having to truly calculate / compute everything. You can use a ton of estimation and logic to save yourself steps while trying to answer these questions.

And this is fantastic! After all, b-school isn’t a math program—and when you do need to do real math, you’ll have Excel. I love that the GMAT keeps moving more and more towards the idea of “Can you think about quantitative topics?” After all, that’s extremely relevant for graduate management education.

Multiple times, I was able to stop solving before getting to the final answer because it was clear that only one answer among the five given could actually work. It almost felt Data Sufficiency-like at times! Try out problems 8 and 9 and tell me where you can stop.

There were multiple opportunities to Work Backwards, in particular on some long Story problem where the answers represented the first number in the story. In that case, we might as well start from the answers and just take the numbers straight on through the story. Try out #22 to see what I mean.

I also saw multiple Max/Min variations. Any problem can be turned into a Maximum or Minimum problem. Basically, I just write a problem that asks you to find the maximum possible value of X (rather than the more common “What is the value of X?”). In this case, while you’re going through the steps of the solution, you’ll have to minimize or maximize other values in order to minimize or maximize the desired ending value. I already referenced #2 as a more straightforward computation problem; it’s also a Max/Min. If you want to see a harder one, try #80.

And if you want to combine Working Backwards and Max / Min, you’re in luck! Try #40.

Overall, of the 35 new questions, 32 of them are numbered 80 or lower—that is, they’re on the easier side of the spectrum. Only 3 problems are up in the 100s and the highest-numbered new problem is #137.

I still do think there are great lessons to learn in these new problems, so don’t neglect them. You’ll be able to pick up some tricks that can help you on other, harder problems in this chapter and elsewhere.

Finally, want to test yourself?

Try #70. This is a lot of work! How can you streamline this? (The official solution shows a longer way to do it.)

Now try #62. Despite the seemingly-low number, I think it can be quite easy to get turned around on this one.

And finally, try the one that I think is the hardest of all of the new PS problems: #55. Is there a good way to make a guess if you can’t figure this one out?

#### Stuck? Here are some hints. Don’t look until you really need to!

#70: Don’t dive right in and start solving. Think about the story; in fact, pretend this is your small business. Make it your story!

You’ve got your costs and your revenues. What do you really care about in business? It’s not the costs or the revenues individually but what they tell you together…

#62: What does it mean to divide by 1/2? What really happens?

#55: Wow, this is a beast. And that’s my first clue. Nobody can calculate this in 2 minutes without a calculator. So there must be some kind of pattern. What’s the pattern?

#### Need another hint? Here you go.

#70: Profits. You have start-up costs of $9,900. And you have profits of$0.55 per unit ($1.20 –$0.65). How can you use the profit figure to streamline the math you need to do?

#62: The problem asks which answer is closest to the given fraction.

#55: Look at the answers. What’s the range of options? Can you get rid of some possibilities?

#### Solutions

#70: I had to sink $9,900 into this business just to get up and running. So how much profit do I need to make until I’ve covered that initial cost? That’s the real question here. For each unit I sell, I make back$0.55. How many units do I need to sell to get to $9,900? Glance at the answers. They’re really far apart. Excellent! Let’s estimate. Let’s say I make$0.50 per unit and I want to make $10,000. I’d need to sell 20,000 units to get there. Is that the answer? Not quite. We estimated, remember? First, we actually only need$9,900, so that’s slightly under 20,000 units. Plus, we’re actually making $0.55 per unit, not just$0.50, so we need even fewer units to make back that initial investment. The next lower number is 18,000, and the one below that is all the way down at 15,000. That’s too low; the answer must be 18,000.

#62: First, re-write. Dividing by 1/2 is the same thing as multiplying by 2.

(7/8 + 1/9)(2)

Next, we could multiply that 2 into the other stuff in the fraction…but that doesn’t actually make it any easier to add up those fractions. I’m still stuck dealing with those different common denominators.

Now, I could do straight up computation here…but the problem asked me what answer is closest to this thing. Why do more work than I have to?

The problem would’ve been a whole lot easier if they’d just given me the same denominators, so let’s make it so. Let’s change 1/9 to the slightly larger fraction 1/8:

(7/8 + 1/8)(2) = (8/8)(2) = (1)(2) = 2

This value is slightly higher than the real value, but not all that much higher. Glance at the answers. 2 is closest.

Are you worried that maybe the fact that we rounded could mean that 3/2 is the answer? By how much did we round in this case?

We went from 1/9 to 1/8; the difference there is a really tiny fraction. That’s not enough to kick the answer all the way down to 3/2, which is a whole 1/2 lower than the number 2. So we’re good here.

#55: Write out the first few values so that you can examine the pattern:

1 + 1/4 + 1/9 + 1/16 + …

Now glance at the answers. It could be 2. Or 3. Or less than 2, between 2 and 3, or greater than 3.

So let’s call 2 and 3 our “anchor” points—the easiest of the possible answers. Can you tell whether the sum can get at least up to 2? Or, if it crosses 2, can you get up to 3?

1 + 1/4 = 1.25. Still have another 0.75 to go.

We’d need another 1/4 just to get up to 1.5. But the next number in the sequence is 1/9, which is less than half of 1/4. So adding 1/9 isn’t even going to get us up to 1.5. Maybe we’re at like 1.3 or 1.35 now? (Pro tip: 1/9 is really close to 1/10. In fact, 1/9 = 11.1%, so technically we’re up to about 1.36 now. But you don’t really need to know that—a rough estimate is good enough.)

Okay, so we’re at 1.35-ish. The next number to add is 1/16, which is even smaller than 1/9. Even if we could add another 1/9 right now, we still wouldn’t get up to 1.5…so we’re maybe at about 1.4 now.

We do keep adding a little bit each time, but that little bit that we add keeps getting smaller and smaller and smaller. The last number added is a minuscule 1/100. So we’re not even going to get up close to 2.