If 'A + B' means 'A' is daughter of 'B', 'A - B' means 'A' is husband of 'B', 'A × B' means 'A' is brother of 'B'. From the statements A × B × C × D', which of the following statement is not necessarily true?

Family tree

Decoding the Symbols:

Given statement: A × B × C × D

Let's break down the relationships:

A × B means 'A is brother of B'. (A is male)

B × C means 'B is brother of C'. (B is male)

C × D means 'C is brother of D'. (C is male)

Now let's check each statement:

1) B is the brother of A - True (If A is brother of B, then B is also a brother of A, as they are siblings and B is male).

2) C is the brother of A - True (If A is brother of B and B is brother of C, then A, B, and C are all siblings and male. Thus, C is the brother of A).

3) D is the brother of C - Not necessarily true (C is the brother of D, but D can be either male (brother) or female (sister)).

4) A, B, C are male - True (The 'X' operation explicitly states the first person is male).

Hence, the statement that is not necessarily true is "Option 3".