 It is currently 15 Jul 2020, 17:38 ### 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

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

#### Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here. # What is the probability that the sum of two different  Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:
Supreme Moderator
Joined: 01 Nov 2017
Posts: 371
Followers: 10

Kudos [?]: 167 , given: 4

What is the probability that the sum of two different [#permalink]
Expert's post 00:00

Question Stats: 50% (01:07) correct 50% (01:36) wrong based on 36 sessions
What is the probability that the sum of two different single-digit prime numbers will NOT be prime?

(A) 0

(B) $$\frac{1}{2}$$

(C) $$\frac{2}{3}$$

(D) $$\frac{5}{6}$$

(E) 1

Diagnostic # 11
[Reveal] Spoiler: OA

_________________

Some useful Theory.
1. Arithmetic and Geometric progressions : https://greprepclub.com/forum/progressions-arithmetic-geometric-and-harmonic-11574.html#p27048
2. Effect of Arithmetic Operations on fraction : https://greprepclub.com/forum/effects-of-arithmetic-operations-on-fractions-11573.html?sid=d570445335a783891cd4d48a17db9825
3. Remainders : https://greprepclub.com/forum/remainders-what-you-should-know-11524.html
4. Number properties : https://greprepclub.com/forum/number-property-all-you-require-11518.html
5. Absolute Modulus and Inequalities : https://greprepclub.com/forum/absolute-modulus-a-better-understanding-11281.html GRE Instructor Joined: 10 Apr 2015
Posts: 3535
Followers: 135

Kudos [?]: 4023  , given: 65

Re: What is the probability that the sum of two different [#permalink]
1
KUDOS
Expert's post
chetan2u wrote:
What is the probability that the sum of two different single-digit prime numbers will NOT be prime?
(A) 0

(B) $$\frac{1}{2}$$

(C) $$\frac{2}{3}$$

(D) $$\frac{5}{6}$$

(E) 1

Diagnostic # 11

Single-digit prime numbers: 2, 3, 5, 7

Since there are so few numbers, we can list all 6 possible combinations.

#1) 2 & 3 (sum = 5)
#2) 2 & 5 (sum = 7)
#3) 2 & 7 (sum = 9)
#4) 3 & 5 (sum = 8)
#5) 3 & 7 (sum = 10)
#6) 5 & 7 (sum = 12)

Of the 6 possible outcomes, 4 outcomes yield a NON-PRIME sum

P(sum is NOT prime) = 4/6 = 2/3

Cheers,
Brent
_________________

Brent Hanneson – Creator of greenlighttestprep.com  Intern Joined: 24 May 2019
Posts: 28
Followers: 0

Kudos [?]: 20  , given: 0

Re: What is the probability that the sum of two different [#permalink]
1
KUDOS
chetan2u wrote:
What is the probability that the sum of two different single-digit prime numbers will NOT be prime?

(A) 0

(B) $$\frac{1}{2}$$

(C) $$\frac{2}{3}$$

(D) $$\frac{5}{6}$$

(E) 1

Diagnostic # 11

-------CONCEPT------------

Single digit prime numbers are
2,3,5,7

Now, except 2 all are odd so we can only get an odd sum if one of our prime number is even while other is odd (Only an odd number can be prime).

2+3 = 5
2+5 = 7
are only 2 cases to satisfy the condition.
while 2 + 7 = 9, it is not prime

& Now the total cases to get a sum by selecting any 2 prime numbers out of these 4 are 4C2 = 6

So, probability for sum NOT to be prime number = 4/6 = 2/3 Re: What is the probability that the sum of two different   [#permalink] 12 Jun 2019, 02:16
Display posts from previous: Sort by

# What is the probability that the sum of two different  Question banks Downloads My Bookmarks Reviews Important topics Powered by phpBB © phpBB Group Kindly note that the GRE® test is a registered trademark of the Educational Testing Service®, and this site has neither been reviewed nor endorsed by ETS®.