Question

Given the b= [1,2,3,4}, how many subsets have exactly two elements

Answer 1

6

{1, 2}, {1, 3}, {1, 4}, {2, 3}, {2, 4}, {3, 4}

Answer 2

6

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

`nC_r=(n!)/(r!(n-r)!)`

We have n=4, r=2

Using the combination formula

`4C_2=(4!)/(2!(4-2)!)`

`4C_2=(4* 3* 2!)/(2!2!)`

`4C_2=(4*3)/(2*1)`=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.