Events & Promotions
|
|
GMAT Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.
Customized
for You
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Apr 2601:30 AM EDT
-02:30 AM EDT
Learn how Keshav, a Chartered Accountant, scored an impressive 705 on GMAT in just 30 days with GMATWhiz's expert guidance. In this video, he shares preparation tips and strategies that worked for him, including the mock, time management, and more.
Apr 2610:00 AM EDT
-11:00 AM EDT
The Target Test Prep course represents a quantum leap forward in GMAT preparation, a radical reinterpretation of the way that students should study. Try before you buy with a 5-day, full-access trial of the course for FREE!
Apr 2512:30 AM EDT
-01:30 AM EDT
At one point, she believed GMAT wasn’t for her. After scoring 595, self-doubt crept in and she questioned her potential. But instead of quitting, she made the right strategic changes. The result? A remarkable comeback to 695. Check out how Saakshi did it.
Apr 2711:00 AM EDT
-12:00 PM EDT
Prefer video-based learning? The Target Test Prep OnDemand course is a one-of-a-kind video masterclass featuring 400 hours of lecture-style teaching by Scott Woodbury-Stewart, founder of Target Test Prep and one of the most accomplished GMAT instructors
Apr 2808:00 AM PDT
-11:00 AM PDT
Whether you are just beginning your MBA journey or fine-tuning your path to a 700+ score, GMAT Day is designed to give you a competitive edge.
May 0111:00 AM PDT
-12:00 PM PDT
Free- full-length test + 15 concept videos + 150+ short videos + study plan!
11 Aug 2019, 05:37
Kudos
Bookmarks
B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
25%
(medium)
Question Stats:
69% (00:54) correct
31%
(01:00)
wrong
based on 107
sessions
History
Date
Time
Result
Not Attempted Yet
The sum of prime numbers that are greater than 50 but less than 60 is
A. 59
B. 112
C. 167
D. 169
E. 220
A. 59
B. 112
C. 167
D. 169
E. 220
11 Aug 2019, 06:56
Kudos
Bookmarks
59 & 53
So,112
Option B
Posted from my mobile device
So,112
Option B
Posted from my mobile device
20 Sep 2019, 00:54
Kudos
Bookmarks
SajjadAhmad
Official Explanation
The key to this question is that we are only talking about 9 numbers that are possibly prime. A formal mathematical approach would be quite difficult, but analysis by cases is easy if we know a few basic rules. There is a finite list of possibilities to consider, so we can start by considering each of these numbers and determining whether or not it's prime.
So, we will start with 51 and count up. The number 51 is divisible by 3, because its digits sum to 6, which is divisible by 3. Then, 52 is even, and the only even prime number is 2, so 52 is not a prime number. The number 53 might be prime. A sure way to test whether a number is prime is to start with a nearby perfect square. 53 is less than 64, which is 8^2. That means we can find out whether 53 is prime by checking all integers from 1 to 8. The reason is this works is that factors come in pairs, so if 53 had a factor above 8, it would be paired with a factor below 8. The number 2 isn't a factor of 53, because 53 is odd. The number 3 isn't a factor, because, the digits of 53 add up to 8, which is not divisible by 3. The number 4, 5, and 6 all also fail to go into 53. You can check each one either by doing long division, or by counting out multiples. For example, 4*12 and 4*13 and 4*14, so 4 is not a factor of 56. Similarly, 7 and 8 are not factors of 53 because they multiply to 56, which is only 3 away. Therefore, 53 is a prime number: its only factors are 1 and itself.
The next few numbers are not prime. Namely, 54 is even, 55 is divisible by 5, 56 is even. The number 57 has digits that sum to 12, which is divisible by 3, so 57 is divisible by 3. Then, 58 is even, so it's not prime. The number 59 might be prime. So for primes, we have 53 and maybe 59. Checking the answer choices, I see that 53 isn't an option, so 59 must be a prime (which we could have confirmed), and the correct answer is 53 + 59 = 112, or (B).
No GMAT question will require you to have memorized primes, but you have to know how to identify whether a number is prime, using the method we just discussed. The method is not much harder for larger numbers. For example, say, on a different question, you want to determine whether the number 111 is prime. The closest perfect squares are 10^2 and 11^2 = 121, so to find out whether 111 is prime, we will have to check at most possible factors from 2 up to 10. As it turns out, in this case we will stop at 3. We can see that 111 is divisible by 3 either by performing long division or by seeing that the digits of 111 sum to a number that is divisible by 3 (in this case, they sum to 3).
Again, the correct answer is (B).
