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Suppose that cardinalities of relations $A$ and $B$ are $m$ and $n$ respectively, then the maximum cardinality of the resultant relation $A \div B$ is ($A$ divides $B$)

(A) $m$                  (B) $m-n$                  (C) $\left \lceil {\frac{m}{n}} \right \rceil$                  (D) $\left \lfloor {\frac{m}{n}} \right \rfloor$
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if A has zero rows, all rows in B will be selected.
So i think A is the correct answer.
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For tuples:

Suppose we have m tuples in A and n tuples in B

Maximum: m

When B has only one tuple and attributes which aren't common has unique (combined) value with common tuples having value same as that in corresponding tuples in B.
Also if B is empty then we will have all m tuples in A in output. ( Attributes will be non-common column between A and B )
Minimum: 0

No tuples satisfy the definition.

For Attributes

Maximum: m

When no attributes of A matches with B.

Minimum: 0 ( not sure)

When all attributes matches
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Cardinality of division operator as A÷B will be A-B

if |A|=m and |B|=n then degree of relatio will be m-n;

One thing very important is that B should subset of A.

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