# Set theory help?

• Sep 26th 2011, 01:33 PM
donuts
Set theory help?
Find 5 elements that could be in:
{x ∈ ℤ|x - 3 ≡ 0 (mod 2) }

Given = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}, find A' given A = {1, 4, 7, 9}
• Sep 26th 2011, 01:49 PM
emakarov
Re: Set theory help?
Are these two different questions? Is the universal set, and is A' the complement of A?

What have you tried and what are your difficulties? Do you understand all the concepts involved?
• Sep 26th 2011, 01:54 PM
donuts
Re: Set theory help?
Quote:

Originally Posted by emakarov
Are these two different questions? Is the universal set, and is A' the complement of A?

What have you tried and what are your difficulties? Do you understand all the concepts involved?

Yes. They're two different questions. I did the first one though. I don't understand the second one. I think we can assume that is just a set that includes 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and that A' is the complement of A.

Also, for the first one, correct me if I'm wrong. I came to the conclusion that basically the elements that could be in there were odd numbers, so I listed odd numbers.
• Sep 26th 2011, 02:01 PM
emakarov
Re: Set theory help?
Quote:

Also, for the first one, correct me if I'm wrong. I came to the conclusion that basically the elements that could be in there were odd numbers, so I listed odd numbers.
I agree.

My guess is that the second question asks to find the complement of {1, 4, 7, 9} when the whole (universal) set is {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}.
• Sep 26th 2011, 02:07 PM
donuts
Re: Set theory help?
Quote:

Originally Posted by emakarov
I agree.

My guess is that the second question asks to find the complement of {1, 4, 7, 9} when the whole (universal) set is {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}.

Yes, that's the conclusion I've come to. Thanks for your time and your help.
• Sep 30th 2011, 04:15 PM
ehpoc
Re: Set theory help?
Quote:

Find 5 elements that could be in:
{x ∈ ℤ|x - 3 ≡ 0 (mod 2) }
Just tagging on here.

Would 13,15,17,19,21 be a correct answer to this question?

Could it not just be any odd number?
• Oct 1st 2011, 02:06 AM
emakarov
Re: Set theory help?
Yes, any odd integer is in the set.