Commanding the Clock on the GMAT
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I watched the Oscar-nominated film Master and Commander when it came out in theaters, and to this day a particularly ghastly scene lingers in my mind.
While fighting through a brutal, sudden storm, the captain of the ship (a very macho Russell Crowe) is forced to make a horrible decision. Two of his men have gone overboard, clinging to a snapped mast floating in the ocean. The mast is still connected to the boat by its rigging, and as the squall blows the boat onward, the deck slowly lists to the side and takes on water, dragged down by the sodden wood and cloth. The men on the mast beg for help, knowing the freezing water is not survivable. But the captain knows that he has seconds before the mast will capsize the boat. Without hesitation, he takes an axe to the ropes, dooming the men in the water but saving the lives of every crew member still aboard.
If you’ve spent any time taking CATs in preparation for your test, you probably already know where I’m going with this. But if you’re new to GMAT prep, here is what you need to know: not only is the GMAT is strictly timed, but is also harshly penalizes unanswered questions at the end of a section. That means that you may have to make the same decision that the Captain did: if a single problem is dragging you down, you have to cut your losses to prevent your ship from sinking.
The signs that it’s time to guess on a problem are clear, though they may require several practice CATs before they become obvious. As a general rule, it’s time to guess if you’ve spend more than a minute looking at any problem without figuring out a how to start solving. Also, you should be aware of the recommended time to answer each question type (2 minutes for Quantitative problems and for Critical Reasoning, 1.5 minutes for Reading Comp questions, 1 minute for Sentence Correction). If you find you’ve doubled the allotted time on a single problem, it’s time to guess even if you feel like you’re ‘close’ to the answer. You’re already behind; you can’t afford to fall behind further.
But unlike the captain, you shouldn’t lose sleep at night for sending problems to an early grave. Remember, the test-makers design the test with guessing in mind. Guessing strategically is the sign of a skilled test-taker, not a struggling one. For one, the GMAT runs on an adaptive algorithm and adjusts to your performance. A super-hard problem that you need to guess on may be a sign that you’re getting your best score ever! Moreover, the test gives you easier questions as a chance to ‘prove yourself’ when you get other questions wrong. You can make for an incorrect guess by nailing those easier questions. But you can’t make up lost time without guessing on another problem—especially if you end up getting the correct solution, making the next adaptive problem even harder. No single problem will get you a good score by itself. Good scores come from getting the most questions right in the most effective manner.
And finally, here is a trick from one of my students to make it easier when it’s time to guess: remind yourself that there are experimental questions. Of course, it’s a sucker’s game to ‘outsmart’ the test by guessing which questions are experimental. But when that nagging feeling of “I can get this one with a few more minutes” is making you hesitate to forge ahead, remind yourself that even if you do spend a few more minutes, and even if you do end up getting the correct answer as a result, there is a small but real chance that the five minutes you spent were for nothing—you could have been clinging to an experimental question all along.
For today’s question of the day, pretend you’re behind schedule. There is a way to narrow the answer choices down two only a few options very quickly. See if you can make an educated guess in under 45 seconds, before you go back to solve it for real. Good luck!
In the figure above, point O is the center of the semicircle, and PQ is parallel to OS.
What is the measure of ∠ROS?
(A) 34°
(B) 36°
(C) 54.5°
(D) 72°
(E) 73°
Solution:
Analyze: What shapes do we see in this mess? A semicircle and three isosceles triangles (we know they’re isosceles because each of them has two sides that are radii of the semicircle).
Because they’re isosceles, what else can we label? We know that for all three triangles, the two “top” angles are equal. So, angle OPQ is 70°, angle OQR is x°, and ORS is x + 1°.
What else does the Q-stem tell us? That PQ is parallel to OS. That means we can find corresponding angles.
Where is a corresponding angle to angle OQP found? Angle QOS. It must also be 70°.
Why might that be of interest? Because PO and QO are both transversals.
Task: Good analysis. What are we being asked for? The measure of angle ROS.
And what do we know about triangles and their internal angles? They sum to 180°. so, < ROS + 2(x +1) = 180.
Approach strategically: All right. We know a lot about triangles QOR and ROS now. What will the sum of their combined angles be? 360. Each triangle has 180°.
Give us an equation that contains all the info we have. 360 = 70 + 4x + 2.
Solve that for x. 360 = 4x + 72 → 288 = 4x → 72 = x.
And how can we use that to calculate angle ROS? 180 = 2(72 + 1) + < ROS → 180 = 146 + < ROS → 34 = < ROS.
Answer (A) is correct.
Confirm: That wasn’t so bad actually. Notice how we used triangles, circles, and even good ol’ lines and angles to get
the solution. Now, what if you didn’t have time for those steps. Is there a guessing strategy available? The triangles
are pretty close and the lines are parallel, so x° must be close to 70°. That would get us down to (a) or (B). Given that
<QOR has angles of x° and < ROS has angles of (x + 1)°, it makes sense to go with (a).
By the way, what’s up with answers (D) and (E)? They’re traps in case we solved for x or (x + 1) instead of what we’re supposed to.
Written by Kaplan GMAT Instructor Eli Meyer.
4 comments
Jesse on February 3rd, 2012 at 1:06 pm
I followed that all the way up to the last part when you wrote "They sum to 180°. so, < ROS + 2(x +1) = 180." A little lost after that. And as a result, doing an educated guess would've done nothing to help. Not sure how many people would've been able to get to that step and gone further.
Santsoh Halemani on February 6th, 2012 at 12:57 am
Awesome article!!
@Jesse: The part where it says ROS+2(x+1) = 180? Its because ROS is an isosceles triangle. Why? RO and SO are radius of the circle hence they are equal. Making ORS and OSR equals. Hope it helped?!
Also I guessed it with splitting the 70 angle by approx half = 35. But got stuck at 34 and 36 answers. How do you go then? Kaplan GMAT any way you can guide me there?
Dp on February 6th, 2012 at 3:57 am
Hi Santsho,
Sum of Two angles of ROS is 2(x+1), and sum of two angles of QOR is 2x. so 3rd angle of ROS is smaller than QOR. Hence angle ROS <angle QOR. so angle ROS=34 and angle QOR = 36
aman on February 7th, 2012 at 11:11 am
Very Helpfull