Answer:
6
Step-by-step explanation:
We are given that a set b={1,2,3,4}
We have to find number of subsets which contain exactly two elements.
Combination formula
[tex]nC_r=\frac{n!}{r!(n-r)!}[/tex]
We have n=4, r=2
Using the combination formula
[tex]4C_2=\frac{4!}{2!(4-2)!}[/tex]
[tex]4C_2=\frac{4\times 3\times 2!}{2!2!}[/tex]
[tex]4C_2=\frac{4\times3}{2\times1}[/tex]=6
Subsets of given set which contain exactly two elements={1,2},{2,3},{3,4},{1,3},{1,4},{2,4}
Hence, 6 subsets of a set which contain exactly two elements.
