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.
Sep 2107:00 PM EDT
-10:00 PM EDT
Boost your GMAT score in less than one month in a live online class + 6 months access to TTP OnDemand video courses included!
16 Nov 2021, 09:22
Kudos
Bookmarks
If \(a\) and \(b\) are positive integers, is \(a*b\) a prime number?
(1) \(b\) is an even number
(2) \(a < 2\)
(1) \(b\) is an even number
(2) \(a < 2\)
16 Nov 2021, 09:22
Kudos
Bookmarks
Official Solution:
If \(a\) and \(b\) are positive integers, is \(a*b\) a prime number?
For \(a*b\) to be a prime, one of the unknowns must be prime and another must be 1.
(1) \(b\) is an even number
If \(b=2\) and \(a=1\), then \(a*b=2=prime\);
If \(b=4\) and \(a=1\), then \(a*b=4 \neq prime\).
Not sufficient.
(2) \(a < 2\)
Since given that \(a\) is a positive integer, then \(a=1\). We don't know anything about \(b\). Not sufficient.
(1)+(2) We got that \(a=1\) and \(b=even\). If \(b=2=prime\), then \(a*b=2=prime\) but if \(b\) is any other even number, then \(a*b\neq prime\). Not sufficient,
Answer: E
If \(a\) and \(b\) are positive integers, is \(a*b\) a prime number?
For \(a*b\) to be a prime, one of the unknowns must be prime and another must be 1.
(1) \(b\) is an even number
If \(b=2\) and \(a=1\), then \(a*b=2=prime\);
If \(b=4\) and \(a=1\), then \(a*b=4 \neq prime\).
Not sufficient.
(2) \(a < 2\)
Since given that \(a\) is a positive integer, then \(a=1\). We don't know anything about \(b\). Not sufficient.
(1)+(2) We got that \(a=1\) and \(b=even\). If \(b=2=prime\), then \(a*b=2=prime\) but if \(b\) is any other even number, then \(a*b\neq prime\). Not sufficient,
Answer: E
