Question

A class Eleventh Maths teacher Khushali wrote some sets in set builder form on a black board of class;A={x: xis a prime natural number and x is less than equal to 7 }

B ={y: y is an odd natural number and y E 7}
Where Universal set U = {l,2,3,4,5,6,7,8}

i)Write sets A and B in roster form
ii)Find A u B and A n B
iii)Find the number of all subsets of universal set U and number of relations from A to B

Answer 1

Explanation:

i)

A = {2, 3, 5, 7}

as "1" can only be divided by one number (instead of the usual 2 numbers for prime numbers), if it's not part of that set.

out of U = {1, 2, 3, 4, 5, 6, 7, 8}

B = {1, 3, 5}

I am not sure what you mean by "y E 7".

I don't think you mean the E7 algebraic group.

I decided you mean y <> 7 (not equal to 7).

ii)

A u B (united) = {1, 2, 3, 5, 7}

A n B (elements in common) = {3, 5}

iii)

a set with n elements has 2^n subsets and (2^n) - 1 proper subsets (all subsets minus the equal one).

our U here has 8 elements, so the number of subsets is

2⁸ = 256.

the number of relations from A to B is 2^|A×B| = 2^(|A|·|B|).

|A| = 4

|B| = 3

so the number of relations from A to B are

2^(4×3) = 2¹² = 4096

remember, for the number of possible relations we have 4×3 = 12 possible combinations of elements of A and engender of B.

each of these combinations can be in the set of relations or not, which gives us 2 options per combination.

that gives us 2¹² relations.