# Thread: Set related question ... find out if disjoint of not disjoint ...

1. ## Set related question ... find out if disjoint of not disjoint ...

Hi,

I am having some problems with SET related questions ... but I am trying ... Maybe someone can help me with this one:

================================
The sets A and B are “disjoint” if:

A B =

Given:
V = { x |1 x 14}
A = { x V|x is a multiple of 2}
B = { x V|x is a multiple of 3}
C = { x V|x is a multiple of 5}
D =

Indicate if the following sets are disjoint or not.

A and B
B and C
A and C
C and D
================================

I know that this is very important to determine the answers:
V = { x |1 x 14}

- x consists of integers ()
- 1 is equal or less then x and x is equal or less then 14

I I am correct D is a set with empty elements and we conclude that "C and D" is a Disjoint right?

Thanks,

2. ## Re: Set related question ... find out if disjoint of not disjoint ...

A and B NOT disjoint since 6 is common.
B and C IS disjoint LCM =15
A and C NOT disjoint since 10 is common

C and D IS disjoint C ∩ ∅ = ∅
for any A

Find the LCM and then see if it is lower than 14.

3. ## Re: Set related question ... find out if disjoint of not disjoint ...

wow ... slow down :-)

How did you get the 6 and the 15 and the 10?

4. ## Re: Set related question ... find out if disjoint of not disjoint ...

Find the Lowest Common Multiple

for example A= 2,4,6,8,10,12,14
B=3,6,9,12

6 is common to both.So it can't be disjoint.
If you write each set out you will see what was common, or find the LCM(shorter method)

Remember that all the numbers in the set A,B,C cannot exceed 14.... therefore B and C are Disjoint, since 15 is common to both

5. ## Re: Set related question ... find out if disjoint of not disjoint ...

anc C would be 5, 10, 15 right?

6. ## Re: Set related question ... find out if disjoint of not disjoint ...

Partly Right, refer to my previous post I edited it

C= 5, 10 remember it cannot exceed 14

7. ## Re: Set related question ... find out if disjoint of not disjoint ...

Originally Posted by iwan1981
anc C would be 5, 10, 15 right?
Remember that all x are elements of V which is V = { x ∈ ℤ|1 ≤ x ≤ 14}

8. ## Re: Set related question ... find out if disjoint of not disjoint ...

Originally Posted by Goku
Remember that all x are elements of V which is V = { x ∈ ℤ|1 ≤ x ≤ 14}
I understand now :-) ...
Thanks!