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If we want to STRENGTHEN an argument, we must first determine how the argument is currently logically flawed, i.e. what information it's missing. Premises: The routine use of antibiotics can give rise to resistant bacteria capable of surviving antibiotic environments Explanation 1: The presence of r...


For more on finding patterns in units digits, see here: https://www.beatthegmat.com/what-is-the-unit-digit-of-the-sum-t297452.html#800962 http://www.beatthegmat.com/remainder-t289535.html#767961 http://www.beatthegmat.com/if-r-s-and-t-are-all-positive-integers-t17201.html#548713 http://www.beatthegm...

by ceilidh.erickson

Tue Jun 11, 2019 12:16 pm
Forum: Data Sufficiency
Topic: If a is an integer, what is the units digit of a^18?
Replies: 2
Views: 801

When dealing with UNITS DIGITS and exponents, we must look for a pattern . If \(a\) is an integer, what is the units digit of \(a^{18}?\) (1) \(a^2\) has a units digit of 9. We can express \(a^{18}\) as \((a^2)^9\) . If \(a^2\) has a units digit of \(9\), then \(a^{18}\) will have the same units dig...

by ceilidh.erickson

Tue Jun 11, 2019 12:09 pm
Forum: Data Sufficiency
Topic: If a is an integer, what is the units digit of a^18?
Replies: 2
Views: 801

Angles opposite one another have the same measurement. Thus, both non-shaded regions measure 45 degrees from the center of the circle, for a total of 90 degrees.

A circle is 360 degrees, so 90 degrees is 1/4 of the circle that is unshaded. That leaves 3/4 of the circle shaded.

The answer is D.


This question is testing PRONOUN AGREEMENT, PARALLELISM, and IDIOMS. Especially in the early years, new entrepreneurs may need to find resourceful ways , like renting temporary office space or using answering services, that make their company seem large and more firmly established than they may actu...


The NUMBER v. PROPORTION flaw is a very common type of logical flaw on CR. For more examples, see: https://www.beatthegmat.com/critical-reasoning-og-13-t277764.html#725229 http://www.beatthegmat.com/i-m-doubting-the-official-answer-of-a-cr-question-t156084.html#551227 http://www.beatthegmat.com/cr-e...


With CR questions, pay particular attention to any arguments that involve the conflation of NUMBERS and PROPORTIONS. Premises: - deer ticks pick up the bacterium while in the larval stage by feeding on infected white-footed mice - certain other species on which the larvae feed do not harbor the bact...


Whenever students tell me "I've been studying for months but I haven't seen any improvement!" usually the missing factor turns out to be that they haven't been REVIEWING deeply. You mention "completing" the OG, but you don't tell us anything else about your study process. To do well on verbal, you n...

by ceilidh.erickson

Tue Jun 11, 2019 10:32 am
Forum: GMAT Verbal & Essays
Topic: How to Improve Score Beyond V32
Replies: 3
Views: 3202

On problems like this, the easiest solution is just to use the answer choices and count the possibilities. Imagine these options for colors: R = red O = orange Y = yellow G = green B = blue P = purple (we'll add more if we need them) For each answer choice, count the options for a single color and f...


(2) \(a\cdot c = 5\) If both of these are integers, it must be 1*5 or 5*1. Since we don't know which is which, though, this is insufficient. Just because this is so important in so many questions: if ac = 5, and a and c are integers, there are four possibilities, not two: a and c can be 5 and 1, in...


This type of 2-variable word problem is know as an EXCHANGE problem, and it can be tricky. For more on exchange problems and translating other tricky word problems, here is a video lesson: https://www.youtube.com/watch?v=5Kg6mjNhLM8&list=PLYZACiD6j3VsFlDR68gbF9CK9gZedcPbY&index=11&t=0s (It's listed ...

by ceilidh.erickson

Sat Jun 01, 2019 10:51 am
Forum: Problem Solving
Topic: Mike has twice as many stamps as Jean has. After he gives
Replies: 2
Views: 696

edit

We can easily translate this algebraically. Let M = Mike's original # of stamps, and J - Jean's original # of stamps. Mike has twice as many stamps as Jean has --> \(M=2J\) After he gives Jean 6 stamps, he still has 8 more stamps than Jean does --> \(M-6=(J+6)+8\) *NB: remember that in an EXCHANGE p...

by ceilidh.erickson

Sat Jun 01, 2019 10:45 am
Forum: Problem Solving
Topic: Mike has twice as many stamps as Jean has. After he gives
Replies: 2
Views: 696

If \(a, b\), and \(c\) are integers, what is the value of \(a\)? We're given no information in the question stem except that these variables are integers. So, we have to dive into the statements: (1) \(2^a+2^b=33\) Think of combinations of powers of 2 that would add to 33. Since 33 is odd, it must b...


Since we're asked what the value is *closest* to, Marty is right - we don't have to do complicated math, we can just estimate with the larger numbers. But, for a lot of exponent questions with addition or subtraction, we can't simply add or subtract the bases, but we can FACTOR: \(10^8-10^2\) ---> \...

by ceilidh.erickson

Sat Jun 01, 2019 10:13 am
Forum: GMAT Math
Topic: GMAT Official Practice Tes #6
Replies: 2
Views: 2415

If one coin flip has a 1/2 chance of landing face up, then the probability that two coin flips will both be face up is \(\frac{1}{2}\cdot\frac{1}{2}=\frac{1}{4}\) Thus, for any M coin flips, the probability of all flips landing face up is \(p=\frac{1}{2^M}\) , and for any N coin flips, the probabili...