Question

If X and Y are two sets such that has 18 elements, X has 8 elements and Y has 15 elements; how many elements does `X nnY`have?

Answer 1

`n(X)=8,n(Y)=15and n(X cupY)=18`
Now `n(X cupY)=n(X)+n(Y)-n(X cap Y)`
`rArr 18=8 + 15 - n(X cap Y)`
`rArr n(X cap Y)=8 +15 - 18 = 5`
Therefore, number of elements in `X cap Y = 5`.