GRE Prep 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.
What is the probability of selecting zeroes from odd rows an
[#permalink]
Updated on: 03 Apr 2019, 09:46
Updated on: 03 Apr 2019, 09:46
3
Bookmarks
00:00
Question Stats:
32% (02:04) correct
68% (02:13) wrong based on 25 sessions
Hide Show timer Statistics
What is the probability of selecting zeroes from odd rows and odd columns?
Show: :: OA
\(\frac{1}{2}\)
Attachments
gre (2).PNG [ 256.71 KiB | Viewed 4915 times ]
GRE Instructor
Joined: 19 Jan 2020
Status:Entrepreneur | GMAT, GRE, CAT, SAT, ACT coach & mentor | Founder @CUBIX | Edu-consulting | Content creator
Posts: 117
Given Kudos: 0
GPA: 3.72
Re: What is the probability of selecting zeroes from odd rows an
[#permalink]
29 Jan 2020, 12:15
29 Jan 2020, 12:15
2
beckhamine wrote:
I think the answer is not 1/2
lets call i the indice number of rows and j the indice number for columns.
As we are looking at the odd numbers, (i,j) are in [1,3,5,7,9].
Now the probability of getting a zero is the probability of having i>= j.
so the number of possibilities to get i>= j when chosing a couple of numbers is 5+4+3+2+1=15.
(if j=1, you have 5 choices, if j=3, you have 4 choices ...)
The number of possibilities is 5*5=25.
So the probability to get a zero is 15/25 = 3/5
lets call i the indice number of rows and j the indice number for columns.
As we are looking at the odd numbers, (i,j) are in [1,3,5,7,9].
Now the probability of getting a zero is the probability of having i>= j.
so the number of possibilities to get i>= j when chosing a couple of numbers is 5+4+3+2+1=15.
(if j=1, you have 5 choices, if j=3, you have 4 choices ...)
The number of possibilities is 5*5=25.
So the probability to get a zero is 15/25 = 3/5
Yes! I think you are correct - also, nice explanation!
For those who did not get it, here is the diagram:
Attachment:
11.JPG [ 38.33 KiB | Viewed 3788 times ]
The shaded boxes are those that belong to odd rows and odd columns
There are 25 such boxes and the number of zeroes is 15
Hence, 15/25 = 3/5 should be the correct answer
General Discussion
Re: What is the probability of selecting zeroes from odd rows an
[#permalink]
14 Dec 2018, 15:12
14 Dec 2018, 15:12
Expert Reply
YMAkib wrote:
What is the probability of selecting zeroes from odd rows and odd columns?
So here we are looking for only odd rows and odd columns.
If you see at an odd row, say 1 - it has one 0 and nine 1s whereas odd column 1 has opposite - one 1 and nine 0s.
Similarly for all other similar numbered rows and columns.
Hence the probability will be 50% or \(\frac{1}{2}\)
