My Math Forum I need help with these question on Sets...

 Applied Math Applied Math Forum

 August 31st, 2010, 10:54 AM #1 Newbie   Joined: Aug 2010 Posts: 13 Thanks: 0 I need help with these question on Sets... Hi, I am currently revising for a Math test with a past exam paper. I'm stuck on question on Sets. I've answered some of them. I was wondering if some can help me work it out. Two sets are defined as follows: A = {n ? ? : ?m ? ? 3m = n} B = {n ? ? : 5 ? n ? 7} 1. Describe, in words, the elements of A. For this I wrote: It is a set of natural numbers. It contains an existential quantification, which has to be a integer of 3 that will equal n. ^^^Am I right with my explanation? If I'm wrong can I get the proper definition of it? 2. Write out explicitly (by listing the elements). a) B = {5,6,7} b) B - A = {2,3,4} c) B ? A = d) B x B = e) ?B = f) $\overline{B}$ where the universal set is {1,2,3,4,5,6,7} = I could only answer two of these. Is is possible some can help me work this out and give me an explanation on how it was worked out? And if it isn't to much hassle can someone make up additional questions so I can go work it on my own, using the explanations that's been given?
August 31st, 2010, 12:22 PM   #2
Global Moderator

Joined: Nov 2006
From: UTC -5

Posts: 16,046
Thanks: 938

Math Focus: Number theory, computational mathematics, combinatorics, FOM, symbolic logic, TCS, algorithms
Re: I need help with these question on Sets...

Quote:
 Originally Posted by Britmouth 1. Describe, in words, the elements of A. For this I wrote: It is a set of natural numbers. It contains an existential quantification, which has to be a integer of 3 that will equal n.
"Positive multiples of 3" would have been my answer.

August 31st, 2010, 12:48 PM   #3
Newbie

Joined: Aug 2010

Posts: 13
Thanks: 0

Re: I need help with these question on Sets...

Quote:
Originally Posted by CRGreathouse
Quote:
 Originally Posted by Britmouth 1. Describe, in words, the elements of A. For this I wrote: It is a set of natural numbers. It contains an existential quantification, which has to be a integer of 3 that will equal n.
"Positive multiples of 3" would have been my answer.
So is what I wrote is right, but just long winded?

August 31st, 2010, 01:11 PM   #4
Global Moderator

Joined: Nov 2006
From: UTC -5

Posts: 16,046
Thanks: 938

Math Focus: Number theory, computational mathematics, combinatorics, FOM, symbolic logic, TCS, algorithms
Re: I need help with these question on Sets...

Quote:
 Originally Posted by Britmouth So is what I wrote is right, but just long winded?
I don't know. It looks like you transliterated the math rather than understood it and rewrote it. It's possible that the teacher would have given credit.

August 31st, 2010, 03:43 PM   #5
Newbie

Joined: Aug 2010

Posts: 13
Thanks: 0

Re: I need help with these question on Sets...

Quote:
Originally Posted by CRGreathouse
Quote:
 Originally Posted by Britmouth So is what I wrote is right, but just long winded?
I don't know. It looks like you transliterated the math rather than understood it and rewrote it. It's possible that the teacher would have given credit.
Ok, thanks. I've worked out a couple more of the questions...

2. Write out explicitly (by listing the elements).
a) B = {5,6,7}
b) B - A = {5,6,7}
c) B ? A = {3,6}
d) B x B = {(5,5),(5,6),(5,7),(6,5),(6,6),(6,7),(7,5),(7,6),( 7,7)}
e) ?B = {Ø,{5},{6},{7},{5,6},{5,7},{6,7},{5,6,7}}
f) $\overline{B}$ where the universal set is {1,2,3,4,5,6,7} =

Can someone check if i'm correct with these? Any=d any help on the last part?

August 31st, 2010, 06:58 PM   #6
Global Moderator

Joined: Nov 2006
From: UTC -5

Posts: 16,046
Thanks: 938

Math Focus: Number theory, computational mathematics, combinatorics, FOM, symbolic logic, TCS, algorithms
Re: I need help with these question on Sets...

Quote:
 Originally Posted by Britmouth 2. Write out explicitly (by listing the elements). a) B = {5,6,7} b) B - A = {5,6,7} c) B ? A = {3,6} d) B x B = {(5,5),(5,6),(5,7),(6,5),(6,6),(6,7),(7,5),(7,6),( 7,7)} e) ?B = {Ø,{5},{6},{7},{5,6},{5,7},{6,7},{5,6,7}} f) $\overline{B}$ where the universal set is {1,2,3,4,5,6,7} = Can someone check if i'm correct with these? Any=d any help on the last part?
Right: a, d, e
Wrong: b, c

f is the same as asking for {1,2,3,4,5,6,7} - B.

 August 31st, 2010, 07:08 PM #7 Global Moderator     Joined: Nov 2009 From: Northwest Arkansas Posts: 2,766 Thanks: 4 Re: I need help with these question on Sets... For b), one of {5,6,7} is in A, so you would have to exclude that element from your answer. The set difference B - A cannot contain any elements in common with A.

 Tags question, sets

 Thread Tools Display Modes Linear Mode

 Similar Threads Thread Thread Starter Forum Replies Last Post maths4computing Applied Math 3 August 25th, 2013 01:30 PM chappyform Real Analysis 2 April 28th, 2013 06:19 PM Hooman Real Analysis 4 July 27th, 2011 04:32 PM sepehr Applied Math 3 April 3rd, 2010 03:46 AM Amir Kiani Applied Math 6 August 29th, 2009 03:33 PM

 Contact - Home - Forums - Cryptocurrency Forum - Top