LaxAvenger wrote:

Hello,

I am refering to problems such as this one:

if-set-b-is-a-subset-of-set-a-how-many-elements-are-in-set-143266.htmlI have no idea to approach them as I don't know about the concept of subsets.

There is no additional theory that you need to know apart from how the sets are formed.

Sets consist of 'elements' that can be related to each other as in {1,2,3,4,5...} or unrelated {1,3,10,50,77...}. Subsets can be any numbr of elements (even 0) from the original set. Null set ({}) is a subset of every set.

For example,

Given set is : {a,b,c}

Subsets are: {}, {a},{b},{c},{a,b} etc

The above questions as well requires the theory mentioned above.

We have been asked how many elements does the main set (A) have if we are given that B is a subset of A.

Now from the example set above ({a,b,c}), we see that if B would have been {a} or {b} or {a,c} etc, then we wouldnt have known the number of elements in A (=3). This is what is mentioned in Statement 1 and is thus not sufficient.

Statement 2 mentions that 80% of the elements in A are not in B. This means that if we have a set {1,2,3,4,5}, B can have 1 element. But if we have a set A as {1,2,3,4,5,6,7,8,9,10}, then B has 2 elements. In other words, 20% of the elements in A are in B. Thus the given information is not sufficient to arrive at an answer.

Combining the 2 statements, we see that B = 14 elements and B is also 20% of elements of A and thus 0.2A=14, thus giving the value of number of elements of A. Thus C is the OA.